<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:01a01003-c811-74d4-b1aa-dab862a5d46a,g:fb59be29-9d33-43bd-ba44-569c6ef3b02d-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://defidevcorp.com/role/CoverPage" xlink:type="simple" xlink:href="dfdv-20260930.xsd#CoverPage"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/CoverPage" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_01a01003-ca29-73ef-b773-7f497e21c2b0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_DocumentInformationTable_01a01003-ca29-73ef-b773-7f497e21c2b0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01a01003-ca29-71ca-a80e-d0bd9ddc8457" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_01a01003-ca29-73ef-b773-7f497e21c2b0" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01a01003-ca29-71ca-a80e-d0bd9ddc8457" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a01003-ca29-71ca-a80e-d0bd9ddc8457_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a01003-ca29-71ca-a80e-d0bd9ddc8457" xlink:to="loc_us-gaap_EquityComponentDomain_01a01003-ca29-71ca-a80e-d0bd9ddc8457_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a01003-ca29-74db-9bd2-cb3579ec808c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a01003-ca29-71ca-a80e-d0bd9ddc8457" xlink:to="loc_us-gaap_EquityComponentDomain_01a01003-ca29-74db-9bd2-cb3579ec808c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_01a01003-ca29-793c-b037-f7096abdd822" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a01003-ca29-74db-9bd2-cb3579ec808c" xlink:to="loc_us-gaap_CommonStockMember_01a01003-ca29-793c-b037-f7096abdd822" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_01a01003-ca29-7c84-ab97-da4a6a3427b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a01003-ca29-74db-9bd2-cb3579ec808c" xlink:to="loc_us-gaap_WarrantMember_01a01003-ca29-7c84-ab97-da4a6a3427b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockMember_01a0f6dc-eec3-76a4-a85a-6a60f1ea3d70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a01003-ca29-74db-9bd2-cb3579ec808c" xlink:to="loc_us-gaap_PreferredStockMember_01a0f6dc-eec3-76a4-a85a-6a60f1ea3d70" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_01a01003-ca29-7797-ae37-c68dac6dd635" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_DocumentType_01a01003-ca29-7797-ae37-c68dac6dd635" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_01a01003-ca29-7da7-b7db-31859a1da99e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_DocumentQuarterlyReport_01a01003-ca29-7da7-b7db-31859a1da99e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_01a01003-ca29-7963-b6b0-74efac74eefd" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_DocumentPeriodEndDate_01a01003-ca29-7963-b6b0-74efac74eefd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_01a01003-ca29-7d0b-8b3e-bba67d40fce3" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_DocumentTransitionReport_01a01003-ca29-7d0b-8b3e-bba67d40fce3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_01a01003-ca29-7cd2-8ecc-83f265739b64" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityFileNumber_01a01003-ca29-7cd2-8ecc-83f265739b64" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_01a01003-ca29-70ae-b18e-dbb263d0b4a8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityRegistrantName_01a01003-ca29-70ae-b18e-dbb263d0b4a8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_01a01003-ca29-7537-989e-408d144f9af9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityIncorporationStateCountryCode_01a01003-ca29-7537-989e-408d144f9af9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_01a01003-ca29-7e22-ae3f-eb852bd92418" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityTaxIdentificationNumber_01a01003-ca29-7e22-ae3f-eb852bd92418" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_01a01003-ca29-7eff-9174-97468309afcd" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityAddressAddressLine1_01a01003-ca29-7eff-9174-97468309afcd" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_01a01003-ca29-7e97-9506-52345ba16517" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityAddressAddressLine2_01a01003-ca29-7e97-9506-52345ba16517" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_01a01003-ca29-764d-b3bd-21aeae3dce6f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityAddressCityOrTown_01a01003-ca29-764d-b3bd-21aeae3dce6f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_01a01003-ca29-78a3-9e44-dac52e864968" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityAddressStateOrProvince_01a01003-ca29-78a3-9e44-dac52e864968" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_01a01003-ca29-7625-9e6c-ee84dfa1f33d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityAddressPostalZipCode_01a01003-ca29-7625-9e6c-ee84dfa1f33d" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_01a01003-ca29-7d4e-91d5-ad42b5d30045" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_CityAreaCode_01a01003-ca29-7d4e-91d5-ad42b5d30045" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_01a01003-ca29-707e-89d3-adbcb666fb3c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_LocalPhoneNumber_01a01003-ca29-707e-89d3-adbcb666fb3c" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_01a01003-ca29-7d40-ba98-dcf1bd752d45" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_Security12bTitle_01a01003-ca29-7d40-ba98-dcf1bd752d45" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_01a01003-ca29-7d1d-a92f-73d640d16edc" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_TradingSymbol_01a01003-ca29-7d1d-a92f-73d640d16edc" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_01a01003-ca29-75b9-aed7-0435eed1ac12" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_SecurityExchangeName_01a01003-ca29-75b9-aed7-0435eed1ac12" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_01a01003-ca29-72e9-9416-907c98626a7e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityCurrentReportingStatus_01a01003-ca29-72e9-9416-907c98626a7e" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_01a01003-ca29-7fba-9312-7e1f12ff88c7" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityInteractiveDataCurrent_01a01003-ca29-7fba-9312-7e1f12ff88c7" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_01a01003-ca29-7c19-8b9d-eeb7f756c3b1" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityFilerCategory_01a01003-ca29-7c19-8b9d-eeb7f756c3b1" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_01a01003-ca29-7481-add0-d4aa79f55b69" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntitySmallBusiness_01a01003-ca29-7481-add0-d4aa79f55b69" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_01a01003-ca29-7404-9bc0-278f6b3078f5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityEmergingGrowthCompany_01a01003-ca29-7404-9bc0-278f6b3078f5" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityExTransitionPeriod_01a01003-ca29-75f2-bea8-ac645cdc6d15" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityExTransitionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityExTransitionPeriod_01a01003-ca29-75f2-bea8-ac645cdc6d15" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_01a01003-ca29-7736-9883-a339422e2a26" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityShellCompany_01a01003-ca29-7736-9883-a339422e2a26" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_01a01003-ca29-7f71-9571-3fa36de30e1d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_01a01003-ca29-7f71-9571-3fa36de30e1d" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_01a01003-ca29-7b12-98d8-2cf109ef18d6" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_AmendmentFlag_01a01003-ca29-7b12-98d8-2cf109ef18d6" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_01a01003-ca29-7636-8c5e-536da8248347" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_DocumentFiscalYearFocus_01a01003-ca29-7636-8c5e-536da8248347" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_01a01003-ca29-7241-977a-60ddfedad54c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_DocumentFiscalPeriodFocus_01a01003-ca29-7241-977a-60ddfedad54c" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_01a01003-ca29-7242-80c5-0782988f9da9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_EntityCentralIndexKey_01a01003-ca29-7242-80c5-0782988f9da9" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_01a01003-ca29-7ed6-9c50-1509daa12a36" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a01003-ca29-79c7-aac7-41bf95056dd4" xlink:to="loc_dei_CurrentFiscalYearEndDate_01a01003-ca29-7ed6-9c50-1509daa12a36" xlink:type="arc" order="30"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="simple" xlink:href="dfdv-20260930.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETS"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a01003-ca29-7296-8d1e-b094d9cc405c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_01a01003-ca29-7415-bd59-723587cf34e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7296-8d1e-b094d9cc405c" xlink:to="loc_us-gaap_StatementTable_01a01003-ca29-7415-bd59-723587cf34e7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_01a01003-ca29-79c4-9458-7bb8927a253f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a01003-ca29-7415-bd59-723587cf34e7" xlink:to="loc_us-gaap_StatementClassOfStockAxis_01a01003-ca29-79c4-9458-7bb8927a253f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-79c4-9458-7bb8927a253f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a01003-ca29-79c4-9458-7bb8927a253f" xlink:to="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-79c4-9458-7bb8927a253f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-717d-81af-570fadffd604" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a01003-ca29-79c4-9458-7bb8927a253f" xlink:to="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-717d-81af-570fadffd604" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_UndesignatedPreferredStockMember_01a01003-ca29-7469-9750-577f5fdcf7f1" xlink:href="dfdv-20260930.xsd#dfdv_UndesignatedPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-717d-81af-570fadffd604" xlink:to="loc_dfdv_UndesignatedPreferredStockMember_01a01003-ca29-7469-9750-577f5fdcf7f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_01a01003-ca29-711b-b1b9-9c762f81803e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-717d-81af-570fadffd604" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_01a01003-ca29-711b-b1b9-9c762f81803e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesBPreferredStockMember_01a01003-ca29-7829-9e39-b7381eca11af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesBPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-717d-81af-570fadffd604" xlink:to="loc_us-gaap_SeriesBPreferredStockMember_01a01003-ca29-7829-9e39-b7381eca11af" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_01a01003-ca29-7e8c-ae59-374da5475e7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7296-8d1e-b094d9cc405c" xlink:to="loc_us-gaap_AssetsAbstract_01a01003-ca29-7e8c-ae59-374da5475e7c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_01a01003-ca29-766b-8c65-65309062fcd3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a01003-ca29-7e8c-ae59-374da5475e7c" xlink:to="loc_us-gaap_AssetsCurrentAbstract_01a01003-ca29-766b-8c65-65309062fcd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_01a01003-ca29-75e0-bd9a-b00a497b998a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_01a01003-ca29-766b-8c65-65309062fcd3" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_01a01003-ca29-75e0-bd9a-b00a497b998a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestments_01a01003-ca29-7da2-b90e-9260e999eb29" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_01a01003-ca29-766b-8c65-65309062fcd3" xlink:to="loc_us-gaap_ShortTermInvestments_01a01003-ca29-7da2-b90e-9260e999eb29" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetsPledgedAsCollateral_01a01003-ca29-7444-911b-7fd53351ffc2" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetsPledgedAsCollateral"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_01a01003-ca29-766b-8c65-65309062fcd3" xlink:to="loc_dfdv_DigitalAssetsPledgedAsCollateral_01a01003-ca29-7444-911b-7fd53351ffc2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredOfferingCosts_01a01003-ca29-7e26-afae-8b1f635793d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredOfferingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_01a01003-ca29-766b-8c65-65309062fcd3" xlink:to="loc_us-gaap_DeferredOfferingCosts_01a01003-ca29-7e26-afae-8b1f635793d1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsCurrent_01a01003-ca29-7cd4-b306-67df82b0c03e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_01a01003-ca29-766b-8c65-65309062fcd3" xlink:to="loc_us-gaap_OtherAssetsCurrent_01a01003-ca29-7cd4-b306-67df82b0c03e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_01a01003-ca29-7571-aa2f-844afa294f73" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_01a01003-ca29-766b-8c65-65309062fcd3" xlink:to="loc_us-gaap_AssetsCurrent_01a01003-ca29-7571-aa2f-844afa294f73" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CryptoAssetFairValueNoncurrent_01a01003-ca29-7bdd-bc01-c2409ddb9988" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CryptoAssetFairValueNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a01003-ca29-7e8c-ae59-374da5475e7c" xlink:to="loc_us-gaap_CryptoAssetFairValueNoncurrent_01a01003-ca29-7bdd-bc01-c2409ddb9988" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetsAtCarryingValueNet_01a01003-ca29-7b7b-8dff-54bf8beb6fbe" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetsAtCarryingValueNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a01003-ca29-7e8c-ae59-374da5475e7c" xlink:to="loc_dfdv_DigitalAssetsAtCarryingValueNet_01a01003-ca29-7b7b-8dff-54bf8beb6fbe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_01a01003-ca29-735e-adab-87d653182c30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a01003-ca29-7e8c-ae59-374da5475e7c" xlink:to="loc_us-gaap_Goodwill_01a01003-ca29-735e-adab-87d653182c30" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_01a01003-ca29-7a11-9992-c16a60879380" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a01003-ca29-7e8c-ae59-374da5475e7c" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_01a01003-ca29-7a11-9992-c16a60879380" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_01a01003-ca29-7b5e-bb5e-9ba57f16cc56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a01003-ca29-7e8c-ae59-374da5475e7c" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_01a01003-ca29-7b5e-bb5e-9ba57f16cc56" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_01a01003-ca29-7664-97b5-1a3ea92ad1dd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a01003-ca29-7e8c-ae59-374da5475e7c" xlink:to="loc_us-gaap_Assets_01a01003-ca29-7664-97b5-1a3ea92ad1dd" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a01003-ca29-74da-841c-e20f87eaeaf4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7296-8d1e-b094d9cc405c" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a01003-ca29-74da-841c-e20f87eaeaf4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_01a01003-ca29-71de-9786-944d7c9c80da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a01003-ca29-74da-841c-e20f87eaeaf4" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_01a01003-ca29-71de-9786-944d7c9c80da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_01a01003-ca29-78aa-b548-565d0b15c071" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a01003-ca29-71de-9786-944d7c9c80da" xlink:to="loc_us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_01a01003-ca29-78aa-b548-565d0b15c071" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetFinancingArrangements_01a01003-ca29-7c29-a2a0-7cc5b6a7a0b1" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetFinancingArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a01003-ca29-71de-9786-944d7c9c80da" xlink:to="loc_dfdv_DigitalAssetFinancingArrangements_01a01003-ca29-7c29-a2a0-7cc5b6a7a0b1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansPayableCurrent_01a01003-ca29-7f0e-8b0d-406351bc8cd0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoansPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a01003-ca29-71de-9786-944d7c9c80da" xlink:to="loc_us-gaap_LoansPayableCurrent_01a01003-ca29-7f0e-8b0d-406351bc8cd0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesCurrent_01a01003-ca29-70d6-bd80-b75c68f4b7f5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a01003-ca29-71de-9786-944d7c9c80da" xlink:to="loc_us-gaap_OtherLiabilitiesCurrent_01a01003-ca29-70d6-bd80-b75c68f4b7f5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_01a01003-ca29-7182-a4e8-1cd97aefced2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_01a01003-ca29-71de-9786-944d7c9c80da" xlink:to="loc_us-gaap_LiabilitiesCurrent_01a01003-ca29-7182-a4e8-1cd97aefced2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_01a01003-ca29-7160-9965-332437630b87" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a01003-ca29-74da-841c-e20f87eaeaf4" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_01a01003-ca29-7160-9965-332437630b87" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_01a01003-ca29-7b0f-b7da-24f34e7c7ca1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a01003-ca29-74da-841c-e20f87eaeaf4" xlink:to="loc_us-gaap_Liabilities_01a01003-ca29-7b0f-b7da-24f34e7c7ca1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_01a01003-ca29-7283-bbab-37302ed164be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a01003-ca29-74da-841c-e20f87eaeaf4" xlink:to="loc_us-gaap_CommitmentsAndContingencies_01a01003-ca29-7283-bbab-37302ed164be" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_MezzanineEquityAbstract_01a16227-04c7-7906-9322-e5cdb874813a" xlink:href="dfdv-20260930.xsd#dfdv_MezzanineEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a01003-ca29-74da-841c-e20f87eaeaf4" xlink:to="loc_dfdv_MezzanineEquityAbstract_01a16227-04c7-7906-9322-e5cdb874813a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityPreferredCarryingAmount_01a185b8-dc7e-7e09-9504-f08d9243473a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RedeemableNoncontrollingInterestEquityPreferredCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dfdv_MezzanineEquityAbstract_01a16227-04c7-7906-9322-e5cdb874813a" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityPreferredCarryingAmount_01a185b8-dc7e-7e09-9504-f08d9243473a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityAbstract_01a01003-ca29-7b87-91de-7bfb5d411ce3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a01003-ca29-74da-841c-e20f87eaeaf4" xlink:to="loc_us-gaap_EquityAbstract_01a01003-ca29-7b87-91de-7bfb5d411ce3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockValue_01a01003-ca29-7532-a4f6-0375d1166d1d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityAbstract_01a01003-ca29-7b87-91de-7bfb5d411ce3" xlink:to="loc_us-gaap_PreferredStockValue_01a01003-ca29-7532-a4f6-0375d1166d1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_01a01003-ca29-7ada-97e0-61abecd27e4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityAbstract_01a01003-ca29-7b87-91de-7bfb5d411ce3" xlink:to="loc_us-gaap_CommonStockValue_01a01003-ca29-7ada-97e0-61abecd27e4c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapital_01a01003-ca29-7200-b245-5569b1fc8ed9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapital"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityAbstract_01a01003-ca29-7b87-91de-7bfb5d411ce3" xlink:to="loc_us-gaap_AdditionalPaidInCapital_01a01003-ca29-7200-b245-5569b1fc8ed9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonValue_01a01003-ca29-7ef5-83d1-284b24b773dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityAbstract_01a01003-ca29-7b87-91de-7bfb5d411ce3" xlink:to="loc_us-gaap_TreasuryStockCommonValue_01a01003-ca29-7ef5-83d1-284b24b773dc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_01a01003-ca29-7a4a-8580-0be8986ecc9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityAbstract_01a01003-ca29-7b87-91de-7bfb5d411ce3" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_01a01003-ca29-7a4a-8580-0be8986ecc9d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_01a01003-ca29-7828-8661-517b3f48e350" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityAbstract_01a01003-ca29-7b87-91de-7bfb5d411ce3" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_01a01003-ca29-7828-8661-517b3f48e350" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a01003-ca29-7682-af5f-25c33773c823" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityAbstract_01a01003-ca29-7b87-91de-7bfb5d411ce3" xlink:to="loc_us-gaap_StockholdersEquity_01a01003-ca29-7682-af5f-25c33773c823" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_01a01003-ca29-7625-ba0e-4be6698b461d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_01a01003-ca29-74da-841c-e20f87eaeaf4" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_01a01003-ca29-7625-ba0e-4be6698b461d" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="simple" xlink:href="dfdv-20260930.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a01003-ca29-7f1e-a06b-7f4b6538f7f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_01a01003-ca29-73d7-944f-dbb33ab0222c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7f1e-a06b-7f4b6538f7f0" xlink:to="loc_us-gaap_StatementTable_01a01003-ca29-73d7-944f-dbb33ab0222c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_01a01003-ca29-727a-a0cd-2c836bf71889" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a01003-ca29-73d7-944f-dbb33ab0222c" xlink:to="loc_us-gaap_StatementClassOfStockAxis_01a01003-ca29-727a-a0cd-2c836bf71889" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-727a-a0cd-2c836bf71889_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a01003-ca29-727a-a0cd-2c836bf71889" xlink:to="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-727a-a0cd-2c836bf71889_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-7914-8562-80a9d5f465b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a01003-ca29-727a-a0cd-2c836bf71889" xlink:to="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-7914-8562-80a9d5f465b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_UndesignatedPreferredStockMember_01a01003-ca29-7704-ae84-201c531e9761" xlink:href="dfdv-20260930.xsd#dfdv_UndesignatedPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-7914-8562-80a9d5f465b6" xlink:to="loc_dfdv_UndesignatedPreferredStockMember_01a01003-ca29-7704-ae84-201c531e9761" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_01a01003-ca29-7d5e-88e5-db6fca9df3bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-7914-8562-80a9d5f465b6" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_01a01003-ca29-7d5e-88e5-db6fca9df3bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesBPreferredStockMember_01a01003-ca29-7bcc-9f87-737f26d0a6cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesBPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-7914-8562-80a9d5f465b6" xlink:to="loc_us-gaap_SeriesBPreferredStockMember_01a01003-ca29-7bcc-9f87-737f26d0a6cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_TemporaryEquityParValuePerShare_01a185bd-4b49-73d0-a823-2924e8bbe361" xlink:href="dfdv-20260930.xsd#dfdv_TemporaryEquityParValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7f1e-a06b-7f4b6538f7f0" xlink:to="loc_dfdv_TemporaryEquityParValuePerShare_01a185bd-4b49-73d0-a823-2924e8bbe361" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_TemporaryEquityStatedValuePerShare_01a19f62-3ef8-7dcd-a36d-1c3dec10a6ef" xlink:href="dfdv-20260930.xsd#dfdv_TemporaryEquityStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7f1e-a06b-7f4b6538f7f0" xlink:to="loc_dfdv_TemporaryEquityStatedValuePerShare_01a19f62-3ef8-7dcd-a36d-1c3dec10a6ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesAuthorized_01a185bd-4b49-7b5d-9925-d49f023b69cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7f1e-a06b-7f4b6538f7f0" xlink:to="loc_us-gaap_TemporaryEquitySharesAuthorized_01a185bd-4b49-7b5d-9925-d49f023b69cb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesIssued_01a185bd-4b49-7bdf-9e51-5568d0566441" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7f1e-a06b-7f4b6538f7f0" xlink:to="loc_us-gaap_TemporaryEquitySharesIssued_01a185bd-4b49-7bdf-9e51-5568d0566441" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_01a185bd-4b49-7478-9ecf-fb2bc98cc83b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7f1e-a06b-7f4b6538f7f0" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_01a185bd-4b49-7478-9ecf-fb2bc98cc83b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_01a01003-ca29-7dae-9879-ccd583b38b7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7f1e-a06b-7f4b6538f7f0" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_01a01003-ca29-7dae-9879-ccd583b38b7c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_01a01003-ca29-75dc-98e9-d6e9ae2e1fd5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7f1e-a06b-7f4b6538f7f0" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_01a01003-ca29-75dc-98e9-d6e9ae2e1fd5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_01a01003-ca29-7389-bd8b-de9c26f0b933" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7f1e-a06b-7f4b6538f7f0" xlink:to="loc_us-gaap_PreferredStockSharesIssued_01a01003-ca29-7389-bd8b-de9c26f0b933" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_01a01003-ca29-76fb-a0db-a8bac5ef635e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7f1e-a06b-7f4b6538f7f0" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_01a01003-ca29-76fb-a0db-a8bac5ef635e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_01a01003-ca29-7888-b869-3db876a0be9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7f1e-a06b-7f4b6538f7f0" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_01a01003-ca29-7888-b869-3db876a0be9d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_01a01003-ca29-71ad-9e95-404118d1e80a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7f1e-a06b-7f4b6538f7f0" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_01a01003-ca29-71ad-9e95-404118d1e80a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_01a01003-ca29-7561-b560-5d5c41cc27a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7f1e-a06b-7f4b6538f7f0" xlink:to="loc_us-gaap_CommonStockSharesIssued_01a01003-ca29-7561-b560-5d5c41cc27a8" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_01a01003-ca29-72da-a56a-99fe784270d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7f1e-a06b-7f4b6538f7f0" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_01a01003-ca29-72da-a56a-99fe784270d8" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="dfdv-20260930.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_01a01003-ca29-7981-a6cc-972cfa2217ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_01a01003-ca29-7279-8a35-e5bdb35886eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7981-a6cc-972cfa2217ae" xlink:to="loc_us-gaap_StatementTable_01a01003-ca29-7279-8a35-e5bdb35886eb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01a01003-ca29-754c-816c-30ffdef7fcfc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a01003-ca29-7279-8a35-e5bdb35886eb" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01a01003-ca29-754c-816c-30ffdef7fcfc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a01003-ca29-754c-816c-30ffdef7fcfc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a01003-ca29-754c-816c-30ffdef7fcfc" xlink:to="loc_us-gaap_EquityComponentDomain_01a01003-ca29-754c-816c-30ffdef7fcfc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a01003-ca29-79a1-9e12-5cef63f4fadf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a01003-ca29-754c-816c-30ffdef7fcfc" xlink:to="loc_us-gaap_EquityComponentDomain_01a01003-ca29-79a1-9e12-5cef63f4fadf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockMember_01a01003-ca29-7712-b13b-db4b8c2909db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a01003-ca29-79a1-9e12-5cef63f4fadf" xlink:to="loc_us-gaap_PreferredStockMember_01a01003-ca29-7712-b13b-db4b8c2909db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_01a01003-ca29-7be4-88f8-c50f9b6f9c56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a01003-ca29-79a1-9e12-5cef63f4fadf" xlink:to="loc_us-gaap_CommonStockMember_01a01003-ca29-7be4-88f8-c50f9b6f9c56" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_01a01003-ca29-733d-a72d-70ab7a467aa6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a01003-ca29-79a1-9e12-5cef63f4fadf" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_01a01003-ca29-733d-a72d-70ab7a467aa6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_01a01003-ca29-76c5-9daf-0582247b8b25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a01003-ca29-79a1-9e12-5cef63f4fadf" xlink:to="loc_us-gaap_TreasuryStockCommonMember_01a01003-ca29-76c5-9daf-0582247b8b25" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a01003-ca29-736a-89d3-2f7762325bb1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a01003-ca29-79a1-9e12-5cef63f4fadf" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a01003-ca29-736a-89d3-2f7762325bb1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_01a01003-ca29-7a4c-9a01-3addc784538e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a01003-ca29-79a1-9e12-5cef63f4fadf" xlink:to="loc_us-gaap_RetainedEarningsMember_01a01003-ca29-7a4c-9a01-3addc784538e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_01a01003-ca29-7c24-add1-8a001b32c51a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_01a01003-ca29-7279-8a35-e5bdb35886eb" xlink:to="loc_us-gaap_StatementClassOfStockAxis_01a01003-ca29-7c24-add1-8a001b32c51a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-7c24-add1-8a001b32c51a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a01003-ca29-7c24-add1-8a001b32c51a" xlink:to="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-7c24-add1-8a001b32c51a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-7ec7-af37-f694c57535e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a01003-ca29-7c24-add1-8a001b32c51a" xlink:to="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-7ec7-af37-f694c57535e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_01a01003-ca29-7dab-9b7e-39a740343154" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a01003-ca29-7ec7-af37-f694c57535e2" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_01a01003-ca29-7dab-9b7e-39a740343154" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_01a01003-ca29-7981-a6cc-972cfa2217ae" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_01a01003-ca29-7e46-8caa-9b13d7eea90e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_SharesOutstanding_01a01003-ca29-7e46-8caa-9b13d7eea90e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a01003-ca29-7aae-be68-cb7cbb4a4535" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_StockholdersEquity_01a01003-ca29-7aae-be68-cb7cbb4a4535" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesOther_01a01003-ca29-7286-9bc5-ad638cfa2870" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesOther_01a01003-ca29-7286-9bc5-ad638cfa2870" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueOther_01a01003-ca29-77fc-8398-3e48ef3c5507" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueOther_01a01003-ca29-77fc-8398-3e48ef3c5507" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_AdjustmentToAdditionalPaidInCapitalPrepaidForwardStockPurchaseDuringPeriodValue_01a0c267-33d9-7041-b34d-7d3d8dbd2571" xlink:href="dfdv-20260930.xsd#dfdv_AdjustmentToAdditionalPaidInCapitalPrepaidForwardStockPurchaseDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_dfdv_AdjustmentToAdditionalPaidInCapitalPrepaidForwardStockPurchaseDuringPeriodValue_01a0c267-33d9-7041-b34d-7d3d8dbd2571" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_StockIssuedDuringPeriodWarrantExercisesShares_01a01003-ca29-7226-af76-fcfebce109a9" xlink:href="dfdv-20260930.xsd#dfdv_StockIssuedDuringPeriodWarrantExercisesShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_dfdv_StockIssuedDuringPeriodWarrantExercisesShares_01a01003-ca29-7226-af76-fcfebce109a9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_StockIssuedDuringPeriodWarrantExercisesValue_01a01003-ca29-7dbb-bd4f-478d85ce1a14" xlink:href="dfdv-20260930.xsd#dfdv_StockIssuedDuringPeriodWarrantExercisesValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_dfdv_StockIssuedDuringPeriodWarrantExercisesValue_01a01003-ca29-7dbb-bd4f-478d85ce1a14" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesPurchaseOfAssets_01a01003-ca29-729e-8d18-e150c46415c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesPurchaseOfAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesPurchaseOfAssets_01a01003-ca29-729e-8d18-e150c46415c1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValuePurchaseOfAssets_01a01003-ca29-7e8a-8762-334ba9ebd912" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValuePurchaseOfAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValuePurchaseOfAssets_01a01003-ca29-7e8a-8762-334ba9ebd912" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_01a01003-ca29-73d8-b2d9-35cfb2bd4f7d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_01a01003-ca29-73d8-b2d9-35cfb2bd4f7d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_01a01003-ca29-7193-a0f2-a0fa131cc9eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_01a01003-ca29-7193-a0f2-a0fa131cc9eb" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_01a01003-ca29-7e47-b536-826b8b8c9ebb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_01a01003-ca29-7e47-b536-826b8b8c9ebb" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_01a01003-ca29-71f1-87f0-74dd53396bf1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_01a01003-ca29-71f1-87f0-74dd53396bf1" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPreferredStockCash_01a16236-04d3-7e24-afd1-f8c52c45f936" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsPreferredStockCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_DividendsPreferredStockCash_01a16236-04d3-7e24-afd1-f8c52c45f936" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_01a01003-ca29-7447-8ae9-431ead2ba285" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_01a01003-ca29-7447-8ae9-431ead2ba285" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_01a01003-ca29-79a4-8a31-c12c5dd79128" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_01a01003-ca29-79a4-8a31-c12c5dd79128" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_01a01003-ca29-7942-8b3c-03fa056c6a03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued_01a01003-ca29-7942-8b3c-03fa056c6a03" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationStockOptionsRequisiteServicePeriodRecognition_01a01003-ca29-7729-a853-3d109c89ed6f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationStockOptionsRequisiteServicePeriodRecognition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationStockOptionsRequisiteServicePeriodRecognition_01a01003-ca29-7729-a853-3d109c89ed6f" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_AdjustmentsToAdditionalPaidInCapitalDiscountOnConvertibleNotes_01a01003-ca29-77fe-8023-0b4415ea4a34" xlink:href="dfdv-20260930.xsd#dfdv_AdjustmentsToAdditionalPaidInCapitalDiscountOnConvertibleNotes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_dfdv_AdjustmentsToAdditionalPaidInCapitalDiscountOnConvertibleNotes_01a01003-ca29-77fe-8023-0b4415ea4a34" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_01a01003-ca29-7c51-a8bd-2a9681e409d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_01a01003-ca29-7c51-a8bd-2a9681e409d8" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_01a01003-ca29-79e8-946d-e18d99a043c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_01a01003-ca29-79e8-946d-e18d99a043c6" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_01a01003-ca29-76df-9716-026044eba552" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_01a01003-ca29-76df-9716-026044eba552" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a01003-ca29-7322-83fa-c7a894091b34" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_01a01003-ca29-7bb3-86ff-9a7f49ee9ac1" xlink:to="loc_us-gaap_NetIncomeLoss_01a01003-ca29-7322-83fa-c7a894091b34" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_01a01003-ca29-74e3-a5bf-63d0c0720e82" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a01003-ca29-7c77-9e98-b38ae88200f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/OVERVIEWANDSIGNIFICANTACCOUNTINGPOLICIESAdditionalInformationDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#OVERVIEWANDSIGNIFICANTACCOUNTINGPOLICIESAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/OVERVIEWANDSIGNIFICANTACCOUNTINGPOLICIESAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_01a01003-ca2a-7435-8324-e9ebc2b0f659" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_01a01003-ca2a-770e-87c8-7ee100d1b1a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_01a01003-ca2a-7435-8324-e9ebc2b0f659" xlink:to="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_01a01003-ca2a-770e-87c8-7ee100d1b1a9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a01003-ca2a-7ee3-b65d-61e8e0b62a79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_01a01003-ca2a-770e-87c8-7ee100d1b1a9" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a01003-ca2a-7ee3-b65d-61e8e0b62a79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a01003-ca2a-7ee3-b65d-61e8e0b62a79_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a01003-ca2a-7ee3-b65d-61e8e0b62a79" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a01003-ca2a-7ee3-b65d-61e8e0b62a79_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a01003-ca2a-7374-b660-0c9ad735ae39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a01003-ca2a-7ee3-b65d-61e8e0b62a79" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a01003-ca2a-7374-b660-0c9ad735ae39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueSegmentMember_01a01003-ca2a-7ab0-bc38-d558e1aea490" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SalesRevenueSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a01003-ca2a-7374-b660-0c9ad735ae39" xlink:to="loc_us-gaap_SalesRevenueSegmentMember_01a01003-ca2a-7ab0-bc38-d558e1aea490" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_01a01003-ca2a-7cbe-b295-19a28a5afeb4" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_01a01003-ca2a-770e-87c8-7ee100d1b1a9" xlink:to="loc_srt_ProductOrServiceAxis_01a01003-ca2a-7cbe-b295-19a28a5afeb4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a01003-ca2a-7cbe-b295-19a28a5afeb4_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_01a01003-ca2a-7cbe-b295-19a28a5afeb4" xlink:to="loc_srt_ProductsAndServicesDomain_01a01003-ca2a-7cbe-b295-19a28a5afeb4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a01003-ca2a-73d2-9822-0f5cf61858fa" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_01a01003-ca2a-7cbe-b295-19a28a5afeb4" xlink:to="loc_srt_ProductsAndServicesDomain_01a01003-ca2a-73d2-9822-0f5cf61858fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetMember_01a01003-ca2a-7d76-9e06-35860a3d2ab0" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a01003-ca2a-73d2-9822-0f5cf61858fa" xlink:to="loc_dfdv_DigitalAssetMember_01a01003-ca2a-7d76-9e06-35860a3d2ab0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_01a01003-ca2a-7ee9-8871-fa91c1ecf081" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCollaborativeArrangementsAndNoncollaborativeArrangementTransactionsTable_01a01003-ca2a-770e-87c8-7ee100d1b1a9" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_01a01003-ca2a-7ee9-8871-fa91c1ecf081" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a01003-ca2a-7ee9-8871-fa91c1ecf081_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a01003-ca2a-7ee9-8871-fa91c1ecf081" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a01003-ca2a-7ee9-8871-fa91c1ecf081_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a01003-ca2a-72ab-9f22-0ac8e9104c64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a01003-ca2a-7ee9-8871-fa91c1ecf081" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a01003-ca2a-72ab-9f22-0ac8e9104c64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductConcentrationRiskMember_01a01003-ca2a-76c4-80ea-6de46ea9b6b8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_01a01003-ca2a-72ab-9f22-0ac8e9104c64" xlink:to="loc_us-gaap_ProductConcentrationRiskMember_01a01003-ca2a-76c4-80ea-6de46ea9b6b8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_OutstandingVotingPowerPercentage_01a01003-ca2a-76e9-b80f-6f3f2776a31c" xlink:href="dfdv-20260930.xsd#dfdv_OutstandingVotingPowerPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_01a01003-ca2a-7435-8324-e9ebc2b0f659" xlink:to="loc_dfdv_OutstandingVotingPowerPercentage_01a01003-ca2a-76e9-b80f-6f3f2776a31c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_01a01003-ca2a-70e5-a07f-47696c867f72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_01a01003-ca2a-7435-8324-e9ebc2b0f659" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_01a01003-ca2a-70e5-a07f-47696c867f72" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/OVERVIEWANDSIGNIFICANTACCOUNTINGPOLICIESScheduleofMarketRiskonDigitalAssetsDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#OVERVIEWANDSIGNIFICANTACCOUNTINGPOLICIESScheduleofMarketRiskonDigitalAssetsDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/OVERVIEWANDSIGNIFICANTACCOUNTINGPOLICIESScheduleofMarketRiskonDigitalAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_01a01003-ca2a-7e5c-bfea-58d01fcf47ba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyTable_01a01003-ca2a-7440-8e4a-ec58739c11b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_01a01003-ca2a-7e5c-bfea-58d01fcf47ba" xlink:to="loc_us-gaap_UnusualRiskOrUncertaintyTable_01a01003-ca2a-7440-8e4a-ec58739c11b7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyByNatureAxis_01a01003-ca2a-732d-ae16-480605d28272" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyByNatureAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyTable_01a01003-ca2a-7440-8e4a-ec58739c11b7" xlink:to="loc_us-gaap_UnusualRiskOrUncertaintyByNatureAxis_01a01003-ca2a-732d-ae16-480605d28272" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyNatureDomain_01a01003-ca2a-732d-ae16-480605d28272_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyByNatureAxis_01a01003-ca2a-732d-ae16-480605d28272" xlink:to="loc_us-gaap_UnusualRiskOrUncertaintyNatureDomain_01a01003-ca2a-732d-ae16-480605d28272_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnusualRiskOrUncertaintyNatureDomain_01a01003-ca2a-76e0-ba00-824ac542e52a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnusualRiskOrUncertaintyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyByNatureAxis_01a01003-ca2a-732d-ae16-480605d28272" xlink:to="loc_us-gaap_UnusualRiskOrUncertaintyNatureDomain_01a01003-ca2a-76e0-ba00-824ac542e52a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_MarketValueRiskMember_01a01003-ca2a-7911-834f-408d4dbb1353" xlink:href="dfdv-20260930.xsd#dfdv_MarketValueRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyNatureDomain_01a01003-ca2a-76e0-ba00-824ac542e52a" xlink:to="loc_dfdv_MarketValueRiskMember_01a01003-ca2a-7911-834f-408d4dbb1353" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CryptoAssetFairValueNoncurrent_01a01003-ca2a-733f-b550-8d053d2072d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CryptoAssetFairValueNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_01a01003-ca2a-7e5c-bfea-58d01fcf47ba" xlink:to="loc_us-gaap_CryptoAssetFairValueNoncurrent_01a01003-ca2a-733f-b550-8d053d2072d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetsAtCarryingValueNet_01a01003-ca2a-7834-917d-c9f2330fa247" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetsAtCarryingValueNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_01a01003-ca2a-7e5c-bfea-58d01fcf47ba" xlink:to="loc_dfdv_DigitalAssetsAtCarryingValueNet_01a01003-ca2a-7834-917d-c9f2330fa247" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetsPledgedAsCollateral_01a01003-ca2a-7c44-a18f-3b901202f13a" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetsPledgedAsCollateral"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_01a01003-ca2a-7e5c-bfea-58d01fcf47ba" xlink:to="loc_dfdv_DigitalAssetsPledgedAsCollateral_01a01003-ca2a-7c44-a18f-3b901202f13a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetFinancingArrangements_01a01003-ca2a-7c4c-a9c9-1490e5ba0144" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetFinancingArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_01a01003-ca2a-7e5c-bfea-58d01fcf47ba" xlink:to="loc_dfdv_DigitalAssetFinancingArrangements_01a01003-ca2a-7c4c-a9c9-1490e5ba0144" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a01003-ca2a-7f63-9225-596af72654bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_UnusualRiskOrUncertaintyLineItems_01a01003-ca2a-7e5c-bfea-58d01fcf47ba" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a01003-ca2a-7f63-9225-596af72654bd" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/REVENUEDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#REVENUEDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/REVENUEDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeLineItems_01a01003-ca2a-7762-a1d3-d3b05265ae96" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_01a01003-ca2a-77cd-8d6f-62e3fab12023" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DeferredIncomeLineItems_01a01003-ca2a-7762-a1d3-d3b05265ae96" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_01a01003-ca2a-77cd-8d6f-62e3fab12023" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_01a01003-ca2a-769f-9573-60a68c78711d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_01a01003-ca2a-77cd-8d6f-62e3fab12023" xlink:to="loc_srt_ProductOrServiceAxis_01a01003-ca2a-769f-9573-60a68c78711d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a01003-ca2a-769f-9573-60a68c78711d_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_01a01003-ca2a-769f-9573-60a68c78711d" xlink:to="loc_srt_ProductsAndServicesDomain_01a01003-ca2a-769f-9573-60a68c78711d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_01a01003-ca2a-7f0c-8473-c353d7e3d1ba" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_01a01003-ca2a-769f-9573-60a68c78711d" xlink:to="loc_srt_ProductsAndServicesDomain_01a01003-ca2a-7f0c-8473-c353d7e3d1ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetTreasuryMember_01a01003-ca2a-759d-9ba4-93d4c599ec04" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetTreasuryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a01003-ca2a-7f0c-8473-c353d7e3d1ba" xlink:to="loc_dfdv_DigitalAssetTreasuryMember_01a01003-ca2a-759d-9ba4-93d4c599ec04" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_RealEstatePlatformMember_01a01003-ca2a-74c8-98dc-ab9de621c985" xlink:href="dfdv-20260930.xsd#dfdv_RealEstatePlatformMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_01a01003-ca2a-7f0c-8473-c353d7e3d1ba" xlink:to="loc_dfdv_RealEstatePlatformMember_01a01003-ca2a-74c8-98dc-ab9de621c985" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a01003-ca2a-7bbd-bcfd-01aa73d6c64b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DeferredIncomeLineItems_01a01003-ca2a-7762-a1d3-d3b05265ae96" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a01003-ca2a-7bbd-bcfd-01aa73d6c64b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/NETINCOMELOSSPERCOMMONSHAREDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#NETINCOMELOSSPERCOMMONSHAREDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/NETINCOMELOSSPERCOMMONSHAREDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a01003-ca2a-791f-a779-8539b28b1a28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_01a01003-ca2a-733d-93f0-6f54d027500c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a01003-ca2a-791f-a779-8539b28b1a28" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_01a01003-ca2a-733d-93f0-6f54d027500c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a01003-ca2a-7eac-a1c3-1f17ac38a021" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_01a01003-ca2a-733d-93f0-6f54d027500c" xlink:to="loc_us-gaap_AwardTypeAxis_01a01003-ca2a-7eac-a1c3-1f17ac38a021" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-ca2a-7eac-a1c3-1f17ac38a021_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_01a01003-ca2a-7eac-a1c3-1f17ac38a021" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-ca2a-7eac-a1c3-1f17ac38a021_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-ca2a-7b61-89c8-2f558e23c672" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_01a01003-ca2a-7eac-a1c3-1f17ac38a021" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-ca2a-7b61-89c8-2f558e23c672" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockCompensationPlanMember_01a01003-ca2a-7787-a345-cf8fe6d81504" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockCompensationPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-ca2a-7b61-89c8-2f558e23c672" xlink:to="loc_us-gaap_StockCompensationPlanMember_01a01003-ca2a-7787-a345-cf8fe6d81504" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_01a01003-ca2a-7287-a79c-7416930f1c5f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-ca2a-7b61-89c8-2f558e23c672" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_01a01003-ca2a-7287-a79c-7416930f1c5f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_ConvertibleNotesMember_01a01003-ca2a-7703-b41b-a8a1233176f2" xlink:href="dfdv-20260930.xsd#dfdv_ConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-ca2a-7b61-89c8-2f558e23c672" xlink:to="loc_dfdv_ConvertibleNotesMember_01a01003-ca2a-7703-b41b-a8a1233176f2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_01a01003-ca2a-7983-b8a7-49252f43e804" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-ca2a-7b61-89c8-2f558e23c672" xlink:to="loc_us-gaap_WarrantMember_01a01003-ca2a-7983-b8a7-49252f43e804" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_01a01003-ca2a-715c-b58d-a4605611b3bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-ca2a-7b61-89c8-2f558e23c672" xlink:to="loc_us-gaap_EmployeeStockOptionMember_01a01003-ca2a-715c-b58d-a4605611b3bc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DividendWarrantMember_01a01003-ca2a-76df-9ea6-e9fe199ae94f" xlink:href="dfdv-20260930.xsd#dfdv_DividendWarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-ca2a-7b61-89c8-2f558e23c672" xlink:to="loc_dfdv_DividendWarrantMember_01a01003-ca2a-76df-9ea6-e9fe199ae94f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAbstract_01a01003-ca2a-7d63-9fef-b2f75c07ce54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a01003-ca2a-791f-a779-8539b28b1a28" xlink:to="loc_us-gaap_NetIncomeLossAbstract_01a01003-ca2a-7d63-9fef-b2f75c07ce54" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_01a1be6a-c578-7e17-a02a-0cb1cee63dfd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAbstract_01a01003-ca2a-7d63-9fef-b2f75c07ce54" xlink:to="loc_us-gaap_NetIncomeLoss_01a1be6a-c578-7e17-a02a-0cb1cee63dfd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockDividendsIncomeStatementImpact_01a185e6-4b9f-76c2-8c65-a8ca16cab05b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockDividendsIncomeStatementImpact"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAbstract_01a01003-ca2a-7d63-9fef-b2f75c07ce54" xlink:to="loc_us-gaap_PreferredStockDividendsIncomeStatementImpact_01a185e6-4b9f-76c2-8c65-a8ca16cab05b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_01a01003-ca2a-7f5e-af27-e5c932c971a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAbstract_01a01003-ca2a-7d63-9fef-b2f75c07ce54" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_01a01003-ca2a-7f5e-af27-e5c932c971a0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_InterestOnConvertibleDebtIncrementalImpact_01a01003-ca2a-7bb7-9d7f-813f5f71cbab" xlink:href="dfdv-20260930.xsd#dfdv_InterestOnConvertibleDebtIncrementalImpact"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAbstract_01a01003-ca2a-7d63-9fef-b2f75c07ce54" xlink:to="loc_dfdv_InterestOnConvertibleDebtIncrementalImpact_01a01003-ca2a-7bb7-9d7f-813f5f71cbab" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_01a01003-ca2a-7c58-8bd6-49c986142222" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAbstract_01a01003-ca2a-7d63-9fef-b2f75c07ce54" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_01a01003-ca2a-7c58-8bd6-49c986142222" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_01a01003-ca2a-7ad4-a138-ef6f0c04e6f9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a01003-ca2a-791f-a779-8539b28b1a28" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_01a01003-ca2a-7ad4-a138-ef6f0c04e6f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_01a01003-ca2a-75b3-9c57-08200a23e4f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_01a01003-ca2a-7ad4-a138-ef6f0c04e6f9" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_01a01003-ca2a-75b3-9c57-08200a23e4f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_01a01003-ca2a-7339-9d10-e2980fe4b87b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_01a01003-ca2a-7ad4-a138-ef6f0c04e6f9" xlink:to="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_01a01003-ca2a-7339-9d10-e2980fe4b87b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_01a01003-ca2a-7d8a-a0f0-7fd7ee75bf5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_01a01003-ca2a-7339-9d10-e2980fe4b87b" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_01a01003-ca2a-7d8a-a0f0-7fd7ee75bf5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities_01a01003-ca2a-7471-a1e2-d884e1110a10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_01a01003-ca2a-7339-9d10-e2980fe4b87b" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities_01a01003-ca2a-7471-a1e2-d884e1110a10" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToCallOptionsAndWarrants_01a01003-ca2a-7c71-bd5c-5657314d2b81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncrementalCommonSharesAttributableToCallOptionsAndWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_01a01003-ca2a-7339-9d10-e2980fe4b87b" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToCallOptionsAndWarrants_01a01003-ca2a-7c71-bd5c-5657314d2b81" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToEquityUnitPurchaseAgreements_01a185cd-5863-7366-886e-c3a75122213f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncrementalCommonSharesAttributableToEquityUnitPurchaseAgreements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_01a01003-ca2a-7339-9d10-e2980fe4b87b" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToEquityUnitPurchaseAgreements_01a185cd-5863-7366-886e-c3a75122213f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_01a01003-ca2a-7fcf-a31a-27763c797bab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingDilutedDisclosureItemsAbstract_01a01003-ca2a-7ad4-a138-ef6f0c04e6f9" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_01a01003-ca2a-7fcf-a31a-27763c797bab" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDilutedOtherDisclosuresAbstract_01a01003-ca2a-7c02-ab17-c1e93f4aa8fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDilutedOtherDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a01003-ca2a-791f-a779-8539b28b1a28" xlink:to="loc_us-gaap_EarningsPerShareDilutedOtherDisclosuresAbstract_01a01003-ca2a-7c02-ab17-c1e93f4aa8fe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_01a01003-ca2a-7e87-b5c7-ac6409db827a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareDilutedOtherDisclosuresAbstract_01a01003-ca2a-7c02-ab17-c1e93f4aa8fe" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_01a01003-ca2a-7e87-b5c7-ac6409db827a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_EarningsPerShareBasicAndDilutedEPSAbstract_01a01003-ca2a-7d68-8abc-69cba699064b" xlink:href="dfdv-20260930.xsd#dfdv_EarningsPerShareBasicAndDilutedEPSAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_01a01003-ca2a-791f-a779-8539b28b1a28" xlink:to="loc_dfdv_EarningsPerShareBasicAndDilutedEPSAbstract_01a01003-ca2a-7d68-8abc-69cba699064b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_01a01003-ca2a-7481-93f0-95c4acfb013b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dfdv_EarningsPerShareBasicAndDilutedEPSAbstract_01a01003-ca2a-7d68-8abc-69cba699064b" xlink:to="loc_us-gaap_EarningsPerShareBasic_01a01003-ca2a-7481-93f0-95c4acfb013b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_01a01003-ca2a-745d-a387-84735aaea7c5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dfdv_EarningsPerShareBasicAndDilutedEPSAbstract_01a01003-ca2a-7d68-8abc-69cba699064b" xlink:to="loc_us-gaap_EarningsPerShareDiluted_01a01003-ca2a-745d-a387-84735aaea7c5" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/SEGMENTSScheduleofSegmentOperatingIncomeLossDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#SEGMENTSScheduleofSegmentOperatingIncomeLossDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/SEGMENTSScheduleofSegmentOperatingIncomeLossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7dba-a601-5aa00409cd6f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a01003-ca2a-723f-9efb-266d2e9bd12e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7dba-a601-5aa00409cd6f" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a01003-ca2a-723f-9efb-266d2e9bd12e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a01003-ca2a-7148-b911-267143385dba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a01003-ca2a-723f-9efb-266d2e9bd12e" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a01003-ca2a-7148-b911-267143385dba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a01003-ca2a-7148-b911-267143385dba_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a01003-ca2a-7148-b911-267143385dba" xlink:to="loc_us-gaap_SegmentDomain_01a01003-ca2a-7148-b911-267143385dba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a01003-ca2a-7d8a-afa8-930af0f891ec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a01003-ca2a-7148-b911-267143385dba" xlink:to="loc_us-gaap_SegmentDomain_01a01003-ca2a-7d8a-afa8-930af0f891ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetTreasuryMember_01a01003-ca2a-7fbd-9fa9-2774f4609abb" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetTreasuryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a01003-ca2a-7d8a-afa8-930af0f891ec" xlink:to="loc_dfdv_DigitalAssetTreasuryMember_01a01003-ca2a-7fbd-9fa9-2774f4609abb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_RealEstatePlatformMember_01a01003-ca2a-701d-97ee-0ce5be63f9b2" xlink:href="dfdv-20260930.xsd#dfdv_RealEstatePlatformMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a01003-ca2a-7d8a-afa8-930af0f891ec" xlink:to="loc_dfdv_RealEstatePlatformMember_01a01003-ca2a-701d-97ee-0ce5be63f9b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a01003-ca2a-741e-ada5-3f4d056c4c09" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7dba-a601-5aa00409cd6f" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a01003-ca2a-741e-ada5-3f4d056c4c09" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_01a01003-ca2a-7079-a958-e20adfbf079e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7dba-a601-5aa00409cd6f" xlink:to="loc_us-gaap_CostOfRevenue_01a01003-ca2a-7079-a958-e20adfbf079e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_01a01003-ca2a-763a-99df-b483ab72b3d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7dba-a601-5aa00409cd6f" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_01a01003-ca2a-763a-99df-b483ab72b3d7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpense_01a01003-ca2a-7606-a95b-8eef41472734" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingAndMarketingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7dba-a601-5aa00409cd6f" xlink:to="loc_us-gaap_SellingAndMarketingExpense_01a01003-ca2a-7606-a95b-8eef41472734" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_01a01003-ca2a-781a-a4b3-63fba7ce5719" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7dba-a601-5aa00409cd6f" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_01a01003-ca2a-781a-a4b3-63fba7ce5719" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_01a01003-ca2a-72b9-aece-fecca44ae96f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7dba-a601-5aa00409cd6f" xlink:to="loc_us-gaap_DepreciationAndAmortization_01a01003-ca2a-72b9-aece-fecca44ae96f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CryptoAssetRealizedAndUnrealizedGainLossOperating_01a01003-ca2a-7428-b765-63926c5f863c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CryptoAssetRealizedAndUnrealizedGainLossOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7dba-a601-5aa00409cd6f" xlink:to="loc_us-gaap_CryptoAssetRealizedAndUnrealizedGainLossOperating_01a01003-ca2a-7428-b765-63926c5f863c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDispositionOfAssets1_01a16244-c8f8-7ec0-9473-03f50fa8763c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnDispositionOfAssets1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7dba-a601-5aa00409cd6f" xlink:to="loc_us-gaap_GainLossOnDispositionOfAssets1_01a16244-c8f8-7ec0-9473-03f50fa8763c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueOptionChangesInFairValueGainLoss1_01a01003-ca2a-7b36-b6b8-7cd2c2992a80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueOptionChangesInFairValueGainLoss1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7dba-a601-5aa00409cd6f" xlink:to="loc_us-gaap_FairValueOptionChangesInFairValueGainLoss1_01a01003-ca2a-7b36-b6b8-7cd2c2992a80" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_01a01003-ca2a-7b10-89ad-0820afa78b75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7dba-a601-5aa00409cd6f" xlink:to="loc_us-gaap_CostsAndExpenses_01a01003-ca2a-7b10-89ad-0820afa78b75" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_01a01003-ca2a-7b31-9da1-af9bd67e2c8b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7dba-a601-5aa00409cd6f" xlink:to="loc_us-gaap_OperatingIncomeLoss_01a01003-ca2a-7b31-9da1-af9bd67e2c8b" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/SEGMENTSScheduleofReconciliationofSegmentIncomeLosstoConsolidatedIncomeLossBeforeIncomeTaxesDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#SEGMENTSScheduleofReconciliationofSegmentIncomeLosstoConsolidatedIncomeLossBeforeIncomeTaxesDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/SEGMENTSScheduleofReconciliationofSegmentIncomeLosstoConsolidatedIncomeLossBeforeIncomeTaxesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a01003-ca2a-7624-93ce-191fb8060518" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a01003-ca2a-7624-93ce-191fb8060518" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_01a01003-ca2a-733b-98b3-3d22eecc5341" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a01003-ca2a-7624-93ce-191fb8060518" xlink:to="loc_srt_ConsolidationItemsAxis_01a01003-ca2a-733b-98b3-3d22eecc5341" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a01003-ca2a-733b-98b3-3d22eecc5341_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_01a01003-ca2a-733b-98b3-3d22eecc5341" xlink:to="loc_srt_ConsolidationItemsDomain_01a01003-ca2a-733b-98b3-3d22eecc5341_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_01a01003-ca2a-752a-a26f-18fef38aa8ea" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_01a01003-ca2a-733b-98b3-3d22eecc5341" xlink:to="loc_srt_ConsolidationItemsDomain_01a01003-ca2a-752a-a26f-18fef38aa8ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_01a01003-ca2a-79a0-9312-40a7cad395dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01a01003-ca2a-752a-a26f-18fef38aa8ea" xlink:to="loc_us-gaap_OperatingSegmentsMember_01a01003-ca2a-79a0-9312-40a7cad395dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_01a01003-ca2a-7ac4-8531-0e72bbceaac9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_01a01003-ca2a-752a-a26f-18fef38aa8ea" xlink:to="loc_us-gaap_CorporateNonSegmentMember_01a01003-ca2a-7ac4-8531-0e72bbceaac9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_01a01003-ca2a-76d6-bd37-476464fb5e80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_01a01003-ca2a-7624-93ce-191fb8060518" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_01a01003-ca2a-76d6-bd37-476464fb5e80" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a01003-ca2a-76d6-bd37-476464fb5e80_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a01003-ca2a-76d6-bd37-476464fb5e80" xlink:to="loc_us-gaap_SegmentDomain_01a01003-ca2a-76d6-bd37-476464fb5e80_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_01a01003-ca2a-7498-b802-37a7f767b021" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_01a01003-ca2a-76d6-bd37-476464fb5e80" xlink:to="loc_us-gaap_SegmentDomain_01a01003-ca2a-7498-b802-37a7f767b021" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_TreasuryMember_01a01003-ca2a-77f0-95ac-5cf6f187600a" xlink:href="dfdv-20260930.xsd#dfdv_TreasuryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a01003-ca2a-7498-b802-37a7f767b021" xlink:to="loc_dfdv_TreasuryMember_01a01003-ca2a-77f0-95ac-5cf6f187600a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_RealEstateInvestmentTrustsMember_01a01003-ca2a-700c-a629-ecfe85310bc5" xlink:href="dfdv-20260930.xsd#dfdv_RealEstateInvestmentTrustsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_01a01003-ca2a-7498-b802-37a7f767b021" xlink:to="loc_dfdv_RealEstateInvestmentTrustsMember_01a01003-ca2a-700c-a629-ecfe85310bc5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a01003-ca2a-7abc-92ea-7b0189b55a1a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_01a01003-ca2a-7abc-92ea-7b0189b55a1a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_01a01003-ca2a-7b26-85f8-c946763b033b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_us-gaap_CostOfRevenue_01a01003-ca2a-7b26-85f8-c946763b033b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpense_01a01003-ca2a-7cb9-976c-e1e31c116f9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpense_01a01003-ca2a-7cb9-976c-e1e31c116f9f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpense_01a01003-ca2a-7076-a658-777ac9b4b303" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingAndMarketingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_us-gaap_SellingAndMarketingExpense_01a01003-ca2a-7076-a658-777ac9b4b303" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_01a01003-ca2a-72c4-834a-25c69e538eae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_01a01003-ca2a-72c4-834a-25c69e538eae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_01a01003-ca2a-79b5-a28b-5179b269bb0f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_us-gaap_DepreciationAndAmortization_01a01003-ca2a-79b5-a28b-5179b269bb0f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CryptoAssetRealizedAndUnrealizedGainLossOperating_01a01003-ca2a-768e-993c-0b943fdffcf3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CryptoAssetRealizedAndUnrealizedGainLossOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_us-gaap_CryptoAssetRealizedAndUnrealizedGainLossOperating_01a01003-ca2a-768e-993c-0b943fdffcf3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDispositionOfAssets1_01a16246-c7fe-7f97-a770-ebe3da66cdc1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnDispositionOfAssets1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_us-gaap_GainLossOnDispositionOfAssets1_01a16246-c7fe-7f97-a770-ebe3da66cdc1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueOptionChangesInFairValueGainLoss1_01a01003-ca2a-77bb-893f-48bb718e8c15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueOptionChangesInFairValueGainLoss1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_us-gaap_FairValueOptionChangesInFairValueGainLoss1_01a01003-ca2a-77bb-893f-48bb718e8c15" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_01a01003-ca2a-7b5d-9e08-49093bfc934b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_us-gaap_CostsAndExpenses_01a01003-ca2a-7b5d-9e08-49093bfc934b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_01a01003-ca2a-7a23-897c-8a0268fc9d61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_us-gaap_OperatingIncomeLoss_01a01003-ca2a-7a23-897c-8a0268fc9d61" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_01a01003-ca2a-7036-8c3f-eddce03da2e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_us-gaap_InterestExpenseNonoperating_01a01003-ca2a-7036-8c3f-eddce03da2e3" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDerivativeInstrumentsHeldForTradingPurposesNet_01a01003-ca2a-7412-b24e-f7f94f94fdfc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainLossOnDerivativeInstrumentsHeldForTradingPurposesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_us-gaap_GainLossOnDerivativeInstrumentsHeldForTradingPurposesNet_01a01003-ca2a-7412-b24e-f7f94f94fdfc" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_01a01003-ca2a-7fb3-a78c-0b218ce4ab54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_01a01003-ca2a-7fb3-a78c-0b218ce4ab54" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_InvestmentAndOtherNonoperatingIncomeExpense_01a01003-ca2a-717f-b311-2f1c4a7c6bf9" xlink:href="dfdv-20260930.xsd#dfdv_InvestmentAndOtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_dfdv_InvestmentAndOtherNonoperatingIncomeExpense_01a01003-ca2a-717f-b311-2f1c4a7c6bf9" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a01003-ca2a-7d67-a11d-b57250cb9810" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_01a01003-ca2a-7b49-9d8f-9bbac99245e7" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_01a01003-ca2a-7d67-a11d-b57250cb9810" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/DIGITALASSETSScheduleofDigitalAssetsatFairValueWithUnitsCostBasisAmountsandFairValueBasedonLevel1InputsDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#DIGITALASSETSScheduleofDigitalAssetsatFairValueWithUnitsCostBasisAmountsandFairValueBasedonLevel1InputsDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/DIGITALASSETSScheduleofDigitalAssetsatFairValueWithUnitsCostBasisAmountsandFairValueBasedonLevel1InputsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CryptoAssetHoldingLineItems_01a01003-ca2a-7724-9d51-d3eccf58f497" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CryptoAssetHoldingLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CryptoAssetHoldingTable_01a01003-ca2a-71c8-8ff0-c081fd35557f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CryptoAssetHoldingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CryptoAssetHoldingLineItems_01a01003-ca2a-7724-9d51-d3eccf58f497" xlink:to="loc_us-gaap_CryptoAssetHoldingTable_01a01003-ca2a-71c8-8ff0-c081fd35557f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CryptoAssetAxis_01a01003-ca2a-73f2-a4cb-6dbfaf25285f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CryptoAssetAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CryptoAssetHoldingTable_01a01003-ca2a-71c8-8ff0-c081fd35557f" xlink:to="loc_srt_CryptoAssetAxis_01a01003-ca2a-73f2-a4cb-6dbfaf25285f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CryptoAssetDomain_01a01003-ca2a-73f2-a4cb-6dbfaf25285f_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CryptoAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CryptoAssetAxis_01a01003-ca2a-73f2-a4cb-6dbfaf25285f" xlink:to="loc_srt_CryptoAssetDomain_01a01003-ca2a-73f2-a4cb-6dbfaf25285f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CryptoAssetDomain_01a01003-ca2a-7bae-8d12-e49894bacf79" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CryptoAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CryptoAssetAxis_01a01003-ca2a-73f2-a4cb-6dbfaf25285f" xlink:to="loc_srt_CryptoAssetDomain_01a01003-ca2a-7bae-8d12-e49894bacf79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_SolanaMember_01a01003-ca2a-730d-a0bc-fff116662b6c" xlink:href="dfdv-20260930.xsd#dfdv_SolanaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CryptoAssetDomain_01a01003-ca2a-7bae-8d12-e49894bacf79" xlink:to="loc_dfdv_SolanaMember_01a01003-ca2a-730d-a0bc-fff116662b6c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CryptoAssetOtherMember_01a01003-ca2a-7e23-b892-68dba8ca0d77" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CryptoAssetOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CryptoAssetDomain_01a01003-ca2a-7bae-8d12-e49894bacf79" xlink:to="loc_srt_CryptoAssetOtherMember_01a01003-ca2a-7e23-b892-68dba8ca0d77" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a01003-ca2a-7e26-a76b-2d867bfe300c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CryptoAssetHoldingTable_01a01003-ca2a-71c8-8ff0-c081fd35557f" xlink:to="loc_srt_RangeAxis_01a01003-ca2a-7e26-a76b-2d867bfe300c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a01003-ca2a-7e26-a76b-2d867bfe300c_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a01003-ca2a-7e26-a76b-2d867bfe300c" xlink:to="loc_srt_RangeMember_01a01003-ca2a-7e26-a76b-2d867bfe300c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a01003-ca2a-71bf-9d06-980cdf76d3ec" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a01003-ca2a-7e26-a76b-2d867bfe300c" xlink:to="loc_srt_RangeMember_01a01003-ca2a-71bf-9d06-980cdf76d3ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a01003-ca2a-77ed-acb9-b96f0c040a63" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a01003-ca2a-71bf-9d06-980cdf76d3ec" xlink:to="loc_srt_MaximumMember_01a01003-ca2a-77ed-acb9-b96f0c040a63" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a01003-ca2a-7158-8f31-e5303cca6be2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CryptoAssetHoldingTable_01a01003-ca2a-71c8-8ff0-c081fd35557f" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a01003-ca2a-7158-8f31-e5303cca6be2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a01003-ca2a-7158-8f31-e5303cca6be2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a01003-ca2a-7158-8f31-e5303cca6be2" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a01003-ca2a-7158-8f31-e5303cca6be2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a01003-ca2a-78ef-880b-69e07fb5b069" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a01003-ca2a-7158-8f31-e5303cca6be2" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a01003-ca2a-78ef-880b-69e07fb5b069" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CryptoAssetOtherMember_01a01003-ca2a-7129-b893-a41f58f65b4e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CryptoAssetOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a01003-ca2a-78ef-880b-69e07fb5b069" xlink:to="loc_srt_CryptoAssetOtherMember_01a01003-ca2a-7129-b893-a41f58f65b4e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_01a01003-ca2a-7f85-a173-fae9b9edcae4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CryptoAssetHoldingTable_01a01003-ca2a-71c8-8ff0-c081fd35557f" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_01a01003-ca2a-7f85-a173-fae9b9edcae4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a01003-ca2a-7f85-a173-fae9b9edcae4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a01003-ca2a-7f85-a173-fae9b9edcae4" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a01003-ca2a-7f85-a173-fae9b9edcae4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a01003-ca2a-7607-95b3-654d07eb8a18" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a01003-ca2a-7f85-a173-fae9b9edcae4" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a01003-ca2a-7607-95b3-654d07eb8a18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductConcentrationRiskMember_01a01003-ca2a-7a93-bb69-97155cfeaa68" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_01a01003-ca2a-7607-95b3-654d07eb8a18" xlink:to="loc_us-gaap_ProductConcentrationRiskMember_01a01003-ca2a-7a93-bb69-97155cfeaa68" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CryptoAssetNumberOfUnits_01a01003-ca2a-7e6a-88e9-a3b74def1fb9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CryptoAssetNumberOfUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CryptoAssetHoldingLineItems_01a01003-ca2a-7724-9d51-d3eccf58f497" xlink:to="loc_us-gaap_CryptoAssetNumberOfUnits_01a01003-ca2a-7e6a-88e9-a3b74def1fb9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CryptoAssetCost_01a01003-ca2a-76e1-9cb5-20310fc95b75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CryptoAssetCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CryptoAssetHoldingLineItems_01a01003-ca2a-7724-9d51-d3eccf58f497" xlink:to="loc_us-gaap_CryptoAssetCost_01a01003-ca2a-76e1-9cb5-20310fc95b75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CryptoAssetFairValue_01a01003-ca2a-7033-a78e-9d6c19f890f0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CryptoAssetFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CryptoAssetHoldingLineItems_01a01003-ca2a-7724-9d51-d3eccf58f497" xlink:to="loc_us-gaap_CryptoAssetFairValue_01a01003-ca2a-7033-a78e-9d6c19f890f0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_01a01003-ca2a-7e92-bba0-fa0298d0cc33" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CryptoAssetHoldingLineItems_01a01003-ca2a-7724-9d51-d3eccf58f497" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_01a01003-ca2a-7e92-bba0-fa0298d0cc33" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/DIGITALASSETSScheduleofFutureReleaseofourLockedSOLInNotionalAmountsCollateralRelatedtoDigitalAssetsFinancingTermLoansDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#DIGITALASSETSScheduleofFutureReleaseofourLockedSOLInNotionalAmountsCollateralRelatedtoDigitalAssetsFinancingTermLoansDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/DIGITALASSETSScheduleofFutureReleaseofourLockedSOLInNotionalAmountsCollateralRelatedtoDigitalAssetsFinancingTermLoansDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CryptoAssetRestrictedLineItems_01a01003-ca2a-7d0b-99df-5757ee4ebea9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CryptoAssetRestrictedLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CryptoAssetRestrictedTable_01a01003-ca2a-7c3c-af4b-8aa9530467e9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CryptoAssetRestrictedTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CryptoAssetRestrictedLineItems_01a01003-ca2a-7d0b-99df-5757ee4ebea9" xlink:to="loc_us-gaap_CryptoAssetRestrictedTable_01a01003-ca2a-7c3c-af4b-8aa9530467e9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CryptoAssetAxis_01a01003-ca2a-7b69-8117-6fd870356e1c" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CryptoAssetAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CryptoAssetRestrictedTable_01a01003-ca2a-7c3c-af4b-8aa9530467e9" xlink:to="loc_srt_CryptoAssetAxis_01a01003-ca2a-7b69-8117-6fd870356e1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CryptoAssetDomain_01a01003-ca2a-7b69-8117-6fd870356e1c_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CryptoAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CryptoAssetAxis_01a01003-ca2a-7b69-8117-6fd870356e1c" xlink:to="loc_srt_CryptoAssetDomain_01a01003-ca2a-7b69-8117-6fd870356e1c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CryptoAssetDomain_01a01003-ca2a-7a40-9381-f29483f66dcb" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CryptoAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CryptoAssetAxis_01a01003-ca2a-7b69-8117-6fd870356e1c" xlink:to="loc_srt_CryptoAssetDomain_01a01003-ca2a-7a40-9381-f29483f66dcb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_SolanaMember_01a01003-ca2a-7a51-8a70-23bff419ba3c" xlink:href="dfdv-20260930.xsd#dfdv_SolanaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CryptoAssetDomain_01a01003-ca2a-7a40-9381-f29483f66dcb" xlink:to="loc_dfdv_SolanaMember_01a01003-ca2a-7a51-8a70-23bff419ba3c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_CryptoAssetNotionalAmountReleaseRemainderOfFiscalYear_01a01003-ca2a-7cee-a46d-d239da565399" xlink:href="dfdv-20260930.xsd#dfdv_CryptoAssetNotionalAmountReleaseRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CryptoAssetRestrictedLineItems_01a01003-ca2a-7d0b-99df-5757ee4ebea9" xlink:to="loc_dfdv_CryptoAssetNotionalAmountReleaseRemainderOfFiscalYear_01a01003-ca2a-7cee-a46d-d239da565399" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_CryptoAssetNotionalAmountReleaseYearOne_01a01003-ca2a-757f-8941-d57fcf2649dc" xlink:href="dfdv-20260930.xsd#dfdv_CryptoAssetNotionalAmountReleaseYearOne"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CryptoAssetRestrictedLineItems_01a01003-ca2a-7d0b-99df-5757ee4ebea9" xlink:to="loc_dfdv_CryptoAssetNotionalAmountReleaseYearOne_01a01003-ca2a-757f-8941-d57fcf2649dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_CryptoAssetNotionalAmountReleaseYearTwo_01a01003-ca2a-79a9-85ab-d0173a17f5dd" xlink:href="dfdv-20260930.xsd#dfdv_CryptoAssetNotionalAmountReleaseYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CryptoAssetRestrictedLineItems_01a01003-ca2a-7d0b-99df-5757ee4ebea9" xlink:to="loc_dfdv_CryptoAssetNotionalAmountReleaseYearTwo_01a01003-ca2a-79a9-85ab-d0173a17f5dd" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/DIGITALASSETSScheduleofDigitalAssetsatCarryingValueWiththeRespectiveGrossandNetCarryingAmountsDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#DIGITALASSETSScheduleofDigitalAssetsatCarryingValueWiththeRespectiveGrossandNetCarryingAmountsDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/DIGITALASSETSScheduleofDigitalAssetsatCarryingValueWiththeRespectiveGrossandNetCarryingAmountsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CryptoAssetHoldingLineItems_01a01003-ca2a-7ab3-b511-8c2acdfb93b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CryptoAssetHoldingLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CryptoAssetHoldingTable_01a01003-ca2a-766f-b55e-2ef9d33f5a7c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CryptoAssetHoldingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CryptoAssetHoldingLineItems_01a01003-ca2a-7ab3-b511-8c2acdfb93b5" xlink:to="loc_us-gaap_CryptoAssetHoldingTable_01a01003-ca2a-766f-b55e-2ef9d33f5a7c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CryptoAssetAxis_01a01003-ca2a-7e3b-b8b9-5ccaf6468dc0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CryptoAssetAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CryptoAssetHoldingTable_01a01003-ca2a-766f-b55e-2ef9d33f5a7c" xlink:to="loc_srt_CryptoAssetAxis_01a01003-ca2a-7e3b-b8b9-5ccaf6468dc0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CryptoAssetDomain_01a01003-ca2a-7e3b-b8b9-5ccaf6468dc0_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CryptoAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CryptoAssetAxis_01a01003-ca2a-7e3b-b8b9-5ccaf6468dc0" xlink:to="loc_srt_CryptoAssetDomain_01a01003-ca2a-7e3b-b8b9-5ccaf6468dc0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CryptoAssetDomain_01a01003-ca2a-7f3b-beab-5c99ec5051cc" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CryptoAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CryptoAssetAxis_01a01003-ca2a-7e3b-b8b9-5ccaf6468dc0" xlink:to="loc_srt_CryptoAssetDomain_01a01003-ca2a-7f3b-beab-5c99ec5051cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_SolanaMember_01a01003-ca2a-76c7-a4c8-25b929ce6fb4" xlink:href="dfdv-20260930.xsd#dfdv_SolanaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CryptoAssetDomain_01a01003-ca2a-7f3b-beab-5c99ec5051cc" xlink:to="loc_dfdv_SolanaMember_01a01003-ca2a-76c7-a4c8-25b929ce6fb4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CryptoAssetOtherMember_01a01003-ca2a-7986-9090-b390535979a8" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CryptoAssetOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CryptoAssetDomain_01a01003-ca2a-7f3b-beab-5c99ec5051cc" xlink:to="loc_srt_CryptoAssetOtherMember_01a01003-ca2a-7986-9090-b390535979a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_01a01003-ca2a-7508-af0a-7b60d5892f9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CryptoAssetHoldingTable_01a01003-ca2a-766f-b55e-2ef9d33f5a7c" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_01a01003-ca2a-7508-af0a-7b60d5892f9f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a01003-ca2a-7508-af0a-7b60d5892f9f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_01a01003-ca2a-7508-af0a-7b60d5892f9f" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a01003-ca2a-7508-af0a-7b60d5892f9f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a01003-ca2a-72d0-a74f-eb9dddc2a4c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_01a01003-ca2a-7508-af0a-7b60d5892f9f" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a01003-ca2a-72d0-a74f-eb9dddc2a4c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a01003-ca2a-789a-905b-7538ae958d9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a01003-ca2a-72d0-a74f-eb9dddc2a4c7" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a01003-ca2a-789a-905b-7538ae958d9d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_01a01003-ca2a-7178-8881-db0ac8b45414" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a01003-ca2a-789a-905b-7538ae958d9d" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_01a01003-ca2a-7178-8881-db0ac8b45414" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a01003-ca2a-71f6-a41b-6bb45454eb37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CryptoAssetHoldingTable_01a01003-ca2a-766f-b55e-2ef9d33f5a7c" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a01003-ca2a-71f6-a41b-6bb45454eb37" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a01003-ca2a-71f6-a41b-6bb45454eb37_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a01003-ca2a-71f6-a41b-6bb45454eb37" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a01003-ca2a-71f6-a41b-6bb45454eb37_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a01003-ca2a-767f-bd7c-d38cf0d8ec36" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_01a01003-ca2a-71f6-a41b-6bb45454eb37" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a01003-ca2a-767f-bd7c-d38cf0d8ec36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CryptoAssetOtherMember_01a01003-ca2a-790c-9a85-fe68deb408f1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CryptoAssetOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_01a01003-ca2a-767f-bd7c-d38cf0d8ec36" xlink:to="loc_srt_CryptoAssetOtherMember_01a01003-ca2a-790c-9a85-fe68deb408f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_01a01003-ca2a-7f81-9bbc-ca27ccb9df4a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CryptoAssetHoldingTable_01a01003-ca2a-766f-b55e-2ef9d33f5a7c" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_01a01003-ca2a-7f81-9bbc-ca27ccb9df4a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a01003-ca2a-7f81-9bbc-ca27ccb9df4a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a01003-ca2a-7f81-9bbc-ca27ccb9df4a" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a01003-ca2a-7f81-9bbc-ca27ccb9df4a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_01a01003-ca2a-7c8b-b826-e5aced0bba92" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_01a01003-ca2a-7f81-9bbc-ca27ccb9df4a" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_01a01003-ca2a-7c8b-b826-e5aced0bba92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductConcentrationRiskMember_01a01003-ca2a-7c63-9229-92f310f757e3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProductConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_01a01003-ca2a-7c8b-b826-e5aced0bba92" xlink:to="loc_us-gaap_ProductConcentrationRiskMember_01a01003-ca2a-7c63-9229-92f310f757e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a01003-ca2a-7cb4-b8af-047745561882" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CryptoAssetHoldingTable_01a01003-ca2a-766f-b55e-2ef9d33f5a7c" xlink:to="loc_srt_RangeAxis_01a01003-ca2a-7cb4-b8af-047745561882" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a01003-ca2a-7cb4-b8af-047745561882_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a01003-ca2a-7cb4-b8af-047745561882" xlink:to="loc_srt_RangeMember_01a01003-ca2a-7cb4-b8af-047745561882_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a01003-ca2a-7593-ab7c-4a8e3f592e37" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a01003-ca2a-7cb4-b8af-047745561882" xlink:to="loc_srt_RangeMember_01a01003-ca2a-7593-ab7c-4a8e3f592e37" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a01003-ca2a-72f3-973d-6543629a47c1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a01003-ca2a-7593-ab7c-4a8e3f592e37" xlink:to="loc_srt_MaximumMember_01a01003-ca2a-72f3-973d-6543629a47c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_CryptoAssetsGross_01a01003-ca2a-7881-a996-68afd00de143" xlink:href="dfdv-20260930.xsd#dfdv_CryptoAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CryptoAssetHoldingLineItems_01a01003-ca2a-7ab3-b511-8c2acdfb93b5" xlink:to="loc_dfdv_CryptoAssetsGross_01a01003-ca2a-7881-a996-68afd00de143" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_CryptoAssetsAccumulatedImpairments_01a01003-ca2a-7409-a1e7-7c0d41ce8966" xlink:href="dfdv-20260930.xsd#dfdv_CryptoAssetsAccumulatedImpairments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CryptoAssetHoldingLineItems_01a01003-ca2a-7ab3-b511-8c2acdfb93b5" xlink:to="loc_dfdv_CryptoAssetsAccumulatedImpairments_01a01003-ca2a-7409-a1e7-7c0d41ce8966" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_CryptoAssetsNet_01a01003-ca2a-7538-a602-88d08bfbfed1" xlink:href="dfdv-20260930.xsd#dfdv_CryptoAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CryptoAssetHoldingLineItems_01a01003-ca2a-7ab3-b511-8c2acdfb93b5" xlink:to="loc_dfdv_CryptoAssetsNet_01a01003-ca2a-7538-a602-88d08bfbfed1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_01a01003-ca2a-7358-a04c-13b2d95ea2a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CryptoAssetHoldingLineItems_01a01003-ca2a-7ab3-b511-8c2acdfb93b5" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_01a01003-ca2a-7358-a04c-13b2d95ea2a9" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/GOODWILLANDINTANGIBLEASSETSScheduleofIntangibleAssetsNetDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#GOODWILLANDINTANGIBLEASSETSScheduleofIntangibleAssetsNetDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/GOODWILLANDINTANGIBLEASSETSScheduleofIntangibleAssetsNetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_IntangibleAssetLineItems_01a01003-ca2a-7381-b75a-e215b62ac01f" xlink:href="dfdv-20260930.xsd#dfdv_IntangibleAssetLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_IntangibleAssetTable_01a01003-ca2a-7b27-beaa-e5e4633bc5e4" xlink:href="dfdv-20260930.xsd#dfdv_IntangibleAssetTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dfdv_IntangibleAssetLineItems_01a01003-ca2a-7381-b75a-e215b62ac01f" xlink:to="loc_dfdv_IntangibleAssetTable_01a01003-ca2a-7b27-beaa-e5e4633bc5e4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a01003-ca2a-7740-b770-364516bc9040" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dfdv_IntangibleAssetTable_01a01003-ca2a-7b27-beaa-e5e4633bc5e4" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a01003-ca2a-7740-b770-364516bc9040" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01003-ca2a-7740-b770-364516bc9040_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a01003-ca2a-7740-b770-364516bc9040" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01003-ca2a-7740-b770-364516bc9040_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01003-ca2a-79e9-a39a-8ed8f9d756b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a01003-ca2a-7740-b770-364516bc9040" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01003-ca2a-79e9-a39a-8ed8f9d756b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_ValidatorMember_01a01003-ca2a-7da8-9233-d8ab6ff92b45" xlink:href="dfdv-20260930.xsd#dfdv_ValidatorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01003-ca2a-79e9-a39a-8ed8f9d756b0" xlink:to="loc_dfdv_ValidatorMember_01a01003-ca2a-7da8-9233-d8ab6ff92b45" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_01a01003-ca2a-7599-bfab-34d4e98c6e9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01003-ca2a-79e9-a39a-8ed8f9d756b0" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_01a01003-ca2a-7599-bfab-34d4e98c6e9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerListsMember_01a01003-ca2a-7248-a529-c8bce7028091" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerListsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a01003-ca2a-79e9-a39a-8ed8f9d756b0" xlink:to="loc_us-gaap_CustomerListsMember_01a01003-ca2a-7248-a529-c8bce7028091" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_01a01003-ca2a-7dd0-86d7-78a218fe1f8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dfdv_IntangibleAssetTable_01a01003-ca2a-7b27-beaa-e5e4633bc5e4" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_01a01003-ca2a-7dd0-86d7-78a218fe1f8e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_01a01003-ca2a-7dd0-86d7-78a218fe1f8e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_01a01003-ca2a-7dd0-86d7-78a218fe1f8e" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_01a01003-ca2a-7dd0-86d7-78a218fe1f8e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_01a01003-ca2a-7c1e-bb8a-32446c3ac172" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_01a01003-ca2a-7dd0-86d7-78a218fe1f8e" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_01a01003-ca2a-7c1e-bb8a-32446c3ac172" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InternetDomainNamesMember_01a01003-ca2a-7be2-9cf8-48485456cfb9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InternetDomainNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_01a01003-ca2a-7c1e-bb8a-32446c3ac172" xlink:to="loc_us-gaap_InternetDomainNamesMember_01a01003-ca2a-7be2-9cf8-48485456cfb9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_01a01003-ca2a-7e7d-816d-e86ac2b101c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNetAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dfdv_IntangibleAssetLineItems_01a01003-ca2a-7381-b75a-e215b62ac01f" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_01a01003-ca2a-7e7d-816d-e86ac2b101c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_01a01003-ca2a-7516-92c4-e465851a9085" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_01a01003-ca2a-7e7d-816d-e86ac2b101c6" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_01a01003-ca2a-7516-92c4-e465851a9085" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_01a01003-ca2a-748c-92c4-3896f2552e12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_01a01003-ca2a-7e7d-816d-e86ac2b101c6" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_01a01003-ca2a-748c-92c4-3896f2552e12" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_01a01003-ca2a-7e05-b22e-383c90da663d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_01a01003-ca2a-7e7d-816d-e86ac2b101c6" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_01a01003-ca2a-7e05-b22e-383c90da663d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_FiniteLivedIntangibleAssetsDisposals_01a01003-ca2a-7f8d-9e59-2bd17deccca1" xlink:href="dfdv-20260930.xsd#dfdv_FiniteLivedIntangibleAssetsDisposals"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_01a01003-ca2a-7e7d-816d-e86ac2b101c6" xlink:to="loc_dfdv_FiniteLivedIntangibleAssetsDisposals_01a01003-ca2a-7f8d-9e59-2bd17deccca1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_01a01003-ca2a-7b9b-927a-258ddcaf1bf1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsNetAbstract_01a01003-ca2a-7e7d-816d-e86ac2b101c6" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_01a01003-ca2a-7b9b-927a-258ddcaf1bf1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract_01a01003-ca2a-7d9b-aed5-1ae7793c0d2c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dfdv_IntangibleAssetLineItems_01a01003-ca2a-7381-b75a-e215b62ac01f" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract_01a01003-ca2a-7d9b-aed5-1ae7793c0d2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_InfiniteLivedIntangibleAssetsGross_01a01003-ca2a-7247-b39b-b76bb0f189d6" xlink:href="dfdv-20260930.xsd#dfdv_InfiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract_01a01003-ca2a-7d9b-aed5-1ae7793c0d2c" xlink:to="loc_dfdv_InfiniteLivedIntangibleAssetsGross_01a01003-ca2a-7247-b39b-b76bb0f189d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_InfiniteLivedIntangibleAssetsAccumulatedAmortization_01a01003-ca2a-7dfe-9714-e21ed94d6436" xlink:href="dfdv-20260930.xsd#dfdv_InfiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract_01a01003-ca2a-7d9b-aed5-1ae7793c0d2c" xlink:to="loc_dfdv_InfiniteLivedIntangibleAssetsAccumulatedAmortization_01a01003-ca2a-7dfe-9714-e21ed94d6436" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_IndefiniteLivedIntangibleAssetsDisposals_01a01003-ca2a-76cb-8c1e-9ded26c7dd32" xlink:href="dfdv-20260930.xsd#dfdv_IndefiniteLivedIntangibleAssetsDisposals"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract_01a01003-ca2a-7d9b-aed5-1ae7793c0d2c" xlink:to="loc_dfdv_IndefiniteLivedIntangibleAssetsDisposals_01a01003-ca2a-76cb-8c1e-9ded26c7dd32" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_01a01003-ca2a-786e-9fe2-21bbce71236d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwillAbstract_01a01003-ca2a-7d9b-aed5-1ae7793c0d2c" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_01a01003-ca2a-786e-9fe2-21bbce71236d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_01a01003-ca2a-75f0-9124-adc02a350a80" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dfdv_IntangibleAssetLineItems_01a01003-ca2a-7381-b75a-e215b62ac01f" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_01a01003-ca2a-75f0-9124-adc02a350a80" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_IntangibleAssetsAccumulatedAmortization_01a01003-ca2a-7e48-927b-bcf8417c396a" xlink:href="dfdv-20260930.xsd#dfdv_IntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dfdv_IntangibleAssetLineItems_01a01003-ca2a-7381-b75a-e215b62ac01f" xlink:to="loc_dfdv_IntangibleAssetsAccumulatedAmortization_01a01003-ca2a-7e48-927b-bcf8417c396a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_IntangibleAssetDisposals_01a01003-ca2a-7dfb-a7eb-cf6744042272" xlink:href="dfdv-20260930.xsd#dfdv_IntangibleAssetDisposals"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dfdv_IntangibleAssetLineItems_01a01003-ca2a-7381-b75a-e215b62ac01f" xlink:to="loc_dfdv_IntangibleAssetDisposals_01a01003-ca2a-7dfb-a7eb-cf6744042272" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_01a01003-ca2a-7f71-800a-50cce187d8c1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dfdv_IntangibleAssetLineItems_01a01003-ca2a-7381-b75a-e215b62ac01f" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_01a01003-ca2a-7f71-800a-50cce187d8c1" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/DEBTScheduleofDebtOutstandingDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#DEBTScheduleofDebtOutstandingDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/DEBTScheduleofDebtOutstandingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-7bfd-9111-c3f1151f94f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_01a01003-ca2a-7769-829b-28466fcda789" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-7bfd-9111-c3f1151f94f7" xlink:to="loc_us-gaap_DebtInstrumentTable_01a01003-ca2a-7769-829b-28466fcda789" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExtinguishmentOfDebtAxis_01a01003-ca2a-7c51-99f4-4796699fcc9d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExtinguishmentOfDebtAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a01003-ca2a-7769-829b-28466fcda789" xlink:to="loc_us-gaap_ExtinguishmentOfDebtAxis_01a01003-ca2a-7c51-99f4-4796699fcc9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_01a01003-ca2a-7c51-99f4-4796699fcc9d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExtinguishmentOfDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ExtinguishmentOfDebtAxis_01a01003-ca2a-7c51-99f4-4796699fcc9d" xlink:to="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_01a01003-ca2a-7c51-99f4-4796699fcc9d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_01a01003-ca2a-772f-be1a-ac1ec04d17ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExtinguishmentOfDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ExtinguishmentOfDebtAxis_01a01003-ca2a-7c51-99f4-4796699fcc9d" xlink:to="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_01a01003-ca2a-772f-be1a-ac1ec04d17ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansPayableMember_01a01003-ca2a-7686-874f-1a087fcdca8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LoansPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_01a01003-ca2a-772f-be1a-ac1ec04d17ac" xlink:to="loc_us-gaap_LoansPayableMember_01a01003-ca2a-7686-874f-1a087fcdca8d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_01a01003-ca2a-7663-ac32-6ecf7b82aec2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a01003-ca2a-7769-829b-28466fcda789" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_01a01003-ca2a-7663-ac32-6ecf7b82aec2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a01003-ca2a-7663-ac32-6ecf7b82aec2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a01003-ca2a-7663-ac32-6ecf7b82aec2" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a01003-ca2a-7663-ac32-6ecf7b82aec2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a01003-ca2a-751b-8f8f-e0464981e473" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a01003-ca2a-7663-ac32-6ecf7b82aec2" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a01003-ca2a-751b-8f8f-e0464981e473" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_01a01003-ca2a-7dc6-814e-8cff41c09180" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a01003-ca2a-751b-8f8f-e0464981e473" xlink:to="loc_us-gaap_ConvertibleDebtMember_01a01003-ca2a-7dc6-814e-8cff41c09180" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a01003-ca2a-71b7-b760-7ab87b2a95ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a01003-ca2a-7769-829b-28466fcda789" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a01003-ca2a-71b7-b760-7ab87b2a95ff" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a01003-ca2a-71b7-b760-7ab87b2a95ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a01003-ca2a-71b7-b760-7ab87b2a95ff" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a01003-ca2a-71b7-b760-7ab87b2a95ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a01003-ca2a-77b9-848b-eca755e33e83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a01003-ca2a-71b7-b760-7ab87b2a95ff" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a01003-ca2a-77b9-848b-eca755e33e83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_AprilTwoThousandThirtyConvertibleNotesMember_01a01003-ca2a-702f-9370-eca22366f465" xlink:href="dfdv-20260930.xsd#dfdv_AprilTwoThousandThirtyConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a01003-ca2a-77b9-848b-eca755e33e83" xlink:to="loc_dfdv_AprilTwoThousandThirtyConvertibleNotesMember_01a01003-ca2a-702f-9370-eca22366f465" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_JulyTwoThousandThirtyConvertibleNotesMember_01a01003-ca2a-76dc-8530-b9e403f0eff9" xlink:href="dfdv-20260930.xsd#dfdv_JulyTwoThousandThirtyConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a01003-ca2a-77b9-848b-eca755e33e83" xlink:to="loc_dfdv_JulyTwoThousandThirtyConvertibleNotesMember_01a01003-ca2a-76dc-8530-b9e403f0eff9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_01a01003-ca2a-7e50-8771-99fb78efd627" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-7bfd-9111-c3f1151f94f7" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_01a01003-ca2a-7e50-8771-99fb78efd627" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a01003-ca2a-7053-b424-6c04f1253419" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-7bfd-9111-c3f1151f94f7" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a01003-ca2a-7053-b424-6c04f1253419" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBorrowingsAbstract_01a01003-ca2a-7f09-b69b-4ca653114fcc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermBorrowingsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-7bfd-9111-c3f1151f94f7" xlink:to="loc_us-gaap_ShortTermBorrowingsAbstract_01a01003-ca2a-7f09-b69b-4ca653114fcc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBorrowings_01a01003-ca2a-7565-b009-f7565664a1f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermBorrowingsAbstract_01a01003-ca2a-7f09-b69b-4ca653114fcc" xlink:to="loc_us-gaap_ShortTermBorrowings_01a01003-ca2a-7565-b009-f7565664a1f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrentAbstract_01a01003-ca2a-7c44-bc5d-a00dbc488315" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-7bfd-9111-c3f1151f94f7" xlink:to="loc_us-gaap_LongTermDebtNoncurrentAbstract_01a01003-ca2a-7c44-bc5d-a00dbc488315" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleLongTermNotesPayable_01a01003-ca2a-7c00-8172-01e02c4f3f4b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleLongTermNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtNoncurrentAbstract_01a01003-ca2a-7c44-bc5d-a00dbc488315" xlink:to="loc_us-gaap_ConvertibleLongTermNotesPayable_01a01003-ca2a-7c00-8172-01e02c4f3f4b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_01a01003-ca2a-7cf8-89ab-3f200efe09b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtNoncurrentAbstract_01a01003-ca2a-7c44-bc5d-a00dbc488315" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_01a01003-ca2a-7cf8-89ab-3f200efe09b7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtNoncurrent_01a01003-ca2a-79bf-97f2-a72493c27e43" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtNoncurrentAbstract_01a01003-ca2a-7c44-bc5d-a00dbc488315" xlink:to="loc_us-gaap_ConvertibleDebtNoncurrent_01a01003-ca2a-79bf-97f2-a72493c27e43" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_01a01003-ca2a-7c9a-9c12-310c06acc3a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtLongtermAndShorttermCombinedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-7bfd-9111-c3f1151f94f7" xlink:to="loc_us-gaap_DebtLongtermAndShorttermCombinedAmount_01a01003-ca2a-7c9a-9c12-310c06acc3a4" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/DEBTAdditionalInformationDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#DEBTAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/DEBTAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-77f3-9dad-2ad3ae8b0545" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_01a01003-ca2a-7bd8-886b-f6e529b52b99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-77f3-9dad-2ad3ae8b0545" xlink:to="loc_us-gaap_DebtInstrumentTable_01a01003-ca2a-7bd8-886b-f6e529b52b99" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExtinguishmentOfDebtAxis_01a01003-ca2a-7493-8e85-1a4dcd561ad0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExtinguishmentOfDebtAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a01003-ca2a-7bd8-886b-f6e529b52b99" xlink:to="loc_us-gaap_ExtinguishmentOfDebtAxis_01a01003-ca2a-7493-8e85-1a4dcd561ad0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_01a01003-ca2a-7493-8e85-1a4dcd561ad0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExtinguishmentOfDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ExtinguishmentOfDebtAxis_01a01003-ca2a-7493-8e85-1a4dcd561ad0" xlink:to="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_01a01003-ca2a-7493-8e85-1a4dcd561ad0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_01a01003-ca2a-78f3-b959-46f1ec07e109" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExtinguishmentOfDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ExtinguishmentOfDebtAxis_01a01003-ca2a-7493-8e85-1a4dcd561ad0" xlink:to="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_01a01003-ca2a-78f3-b959-46f1ec07e109" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtMember_01a01003-ca2a-7d29-bb74-a6be6aec5b10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ExtinguishmentOfDebtTypeDomain_01a01003-ca2a-78f3-b959-46f1ec07e109" xlink:to="loc_us-gaap_ShortTermDebtMember_01a01003-ca2a-7d29-bb74-a6be6aec5b10" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_01a01003-ca2a-72a8-bf9a-a045f25a724e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a01003-ca2a-7bd8-886b-f6e529b52b99" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_01a01003-ca2a-72a8-bf9a-a045f25a724e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a01003-ca2a-72a8-bf9a-a045f25a724e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a01003-ca2a-72a8-bf9a-a045f25a724e" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a01003-ca2a-72a8-bf9a-a045f25a724e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a01003-ca2a-713e-a826-200e0ad3b810" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a01003-ca2a-72a8-bf9a-a045f25a724e" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a01003-ca2a-713e-a826-200e0ad3b810" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_01a01003-ca2a-7858-944f-17f16380ae2a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a01003-ca2a-713e-a826-200e0ad3b810" xlink:to="loc_us-gaap_ConvertibleDebtMember_01a01003-ca2a-7858-944f-17f16380ae2a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a01003-ca2a-724b-8653-9e52dfc730f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_01a01003-ca2a-7bd8-886b-f6e529b52b99" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a01003-ca2a-724b-8653-9e52dfc730f8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a01003-ca2a-724b-8653-9e52dfc730f8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a01003-ca2a-724b-8653-9e52dfc730f8" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a01003-ca2a-724b-8653-9e52dfc730f8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a01003-ca2a-7145-8350-8702a9407077" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a01003-ca2a-724b-8653-9e52dfc730f8" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a01003-ca2a-7145-8350-8702a9407077" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_JulyTwoThousandThirtyConvertibleNotesMember_01a01003-ca2a-7ee1-944e-cac0cc8bdbb3" xlink:href="dfdv-20260930.xsd#dfdv_JulyTwoThousandThirtyConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a01003-ca2a-7145-8350-8702a9407077" xlink:to="loc_dfdv_JulyTwoThousandThirtyConvertibleNotesMember_01a01003-ca2a-7ee1-944e-cac0cc8bdbb3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_AprilTwoThousandThirtyConvertibleNotesMember_01a01003-ca2a-734e-bae5-1bcd4d3f01dd" xlink:href="dfdv-20260930.xsd#dfdv_AprilTwoThousandThirtyConvertibleNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a01003-ca2a-7145-8350-8702a9407077" xlink:to="loc_dfdv_AprilTwoThousandThirtyConvertibleNotesMember_01a01003-ca2a-734e-bae5-1bcd4d3f01dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_01a01003-ca2a-7b71-8ca6-975c62f77b8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-77f3-9dad-2ad3ae8b0545" xlink:to="loc_us-gaap_LongTermDebtFairValue_01a01003-ca2a-7b71-8ca6-975c62f77b8f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_BorrowingForDirectorAndOfficerInsurancePolicy_01a01003-ca2a-7934-aa10-064a40d514f6" xlink:href="dfdv-20260930.xsd#dfdv_BorrowingForDirectorAndOfficerInsurancePolicy"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-77f3-9dad-2ad3ae8b0545" xlink:to="loc_dfdv_BorrowingForDirectorAndOfficerInsurancePolicy_01a01003-ca2a-7934-aa10-064a40d514f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_01a01003-ca2a-718a-9d0e-c338bb731240" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-77f3-9dad-2ad3ae8b0545" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_01a01003-ca2a-718a-9d0e-c338bb731240" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_InsurancePremiumsPayableTerm_01a01003-ca2a-7b84-b008-e1a9edcf12d6" xlink:href="dfdv-20260930.xsd#dfdv_InsurancePremiumsPayableTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-77f3-9dad-2ad3ae8b0545" xlink:to="loc_dfdv_InsurancePremiumsPayableTerm_01a01003-ca2a-7b84-b008-e1a9edcf12d6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a01003-ca2a-7759-bdc3-5d4df7ac0c59" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-77f3-9dad-2ad3ae8b0545" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a01003-ca2a-7759-bdc3-5d4df7ac0c59" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_PaymentForInsurancePolicy_01a01003-ca2a-745e-b4ae-49a82b8d67ff" xlink:href="dfdv-20260930.xsd#dfdv_PaymentForInsurancePolicy"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-77f3-9dad-2ad3ae8b0545" xlink:to="loc_dfdv_PaymentForInsurancePolicy_01a01003-ca2a-745e-b4ae-49a82b8d67ff" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleNotesPayable_01a01003-ca2a-7e21-a20c-a566310acd28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-77f3-9dad-2ad3ae8b0545" xlink:to="loc_us-gaap_ConvertibleNotesPayable_01a01003-ca2a-7e21-a20c-a566310acd28" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfConvertibleDebt_01a01003-ca2a-7e58-95d5-c67523e9e728" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-77f3-9dad-2ad3ae8b0545" xlink:to="loc_us-gaap_RepaymentsOfConvertibleDebt_01a01003-ca2a-7e58-95d5-c67523e9e728" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_01a01003-ca2a-7b23-be00-0adc31c96786" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentRepurchasedFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-77f3-9dad-2ad3ae8b0545" xlink:to="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_01a01003-ca2a-7b23-be00-0adc31c96786" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_01a01003-ca2a-771c-b124-df365664fe0f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01a01003-ca2a-77f3-9dad-2ad3ae8b0545" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_01a01003-ca2a-771c-b124-df365664fe0f" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/DERIVATIVESScheduleofDerivativeAssetsandLiabilitiesDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#DERIVATIVESScheduleofDerivativeAssetsandLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/DERIVATIVESScheduleofDerivativeAssetsandLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_01a01003-ca2a-7819-b317-ce0f8bf3391a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_01a01003-ca2a-70ef-8542-052a11b5d188" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_01a01003-ca2a-7819-b317-ce0f8bf3391a" xlink:to="loc_us-gaap_DerivativeTable_01a01003-ca2a-70ef-8542-052a11b5d188" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_01a01003-ca2a-7dc5-b082-4692b095a333" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a01003-ca2a-70ef-8542-052a11b5d188" xlink:to="loc_us-gaap_HedgingDesignationAxis_01a01003-ca2a-7dc5-b082-4692b095a333" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a01003-ca2a-7dc5-b082-4692b095a333_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a01003-ca2a-7dc5-b082-4692b095a333" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a01003-ca2a-7dc5-b082-4692b095a333_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a01003-ca2a-78d3-80a4-c4e0a7f327bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a01003-ca2a-7dc5-b082-4692b095a333" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a01003-ca2a-78d3-80a4-c4e0a7f327bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_01a01003-ca2a-74ed-9351-2e6908b13397" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_01a01003-ca2a-78d3-80a4-c4e0a7f327bd" xlink:to="loc_us-gaap_NondesignatedMember_01a01003-ca2a-74ed-9351-2e6908b13397" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a01003-ca2a-7ede-8164-939d5d13248e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a01003-ca2a-70ef-8542-052a11b5d188" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a01003-ca2a-7ede-8164-939d5d13248e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a01003-ca2a-7ede-8164-939d5d13248e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a01003-ca2a-7ede-8164-939d5d13248e" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a01003-ca2a-7ede-8164-939d5d13248e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a01003-ca2a-79d9-aa6c-5fe63debebaf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a01003-ca2a-7ede-8164-939d5d13248e" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a01003-ca2a-79d9-aa6c-5fe63debebaf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetsPledgedAsCollateralMember_01a01003-ca2a-7907-81d5-427c32082732" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetsPledgedAsCollateralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a01003-ca2a-79d9-aa6c-5fe63debebaf" xlink:to="loc_dfdv_DigitalAssetsPledgedAsCollateralMember_01a01003-ca2a-7907-81d5-427c32082732" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetFinancingArrangementsMember_01a01003-ca2a-787c-b00d-5f64fbb4c9af" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetFinancingArrangementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a01003-ca2a-79d9-aa6c-5fe63debebaf" xlink:to="loc_dfdv_DigitalAssetFinancingArrangementsMember_01a01003-ca2a-787c-b00d-5f64fbb4c9af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_AccountsPayableAndAccruedExpensesMember_01a1869f-024f-7088-b289-64fcf67c459f" xlink:href="dfdv-20260930.xsd#dfdv_AccountsPayableAndAccruedExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a01003-ca2a-79d9-aa6c-5fe63debebaf" xlink:to="loc_dfdv_AccountsPayableAndAccruedExpensesMember_01a1869f-024f-7088-b289-64fcf67c459f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssets_01a01003-ca2a-7daf-b1c1-11b8ce6667d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a01003-ca2a-7819-b317-ce0f8bf3391a" xlink:to="loc_us-gaap_DerivativeAssets_01a01003-ca2a-7daf-b1c1-11b8ce6667d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetStatementOfFinancialPositionExtensibleEnumeration_01a01003-ca2a-7ce4-a15b-40072a533266" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeAssetStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a01003-ca2a-7819-b317-ce0f8bf3391a" xlink:to="loc_us-gaap_DerivativeAssetStatementOfFinancialPositionExtensibleEnumeration_01a01003-ca2a-7ce4-a15b-40072a533266" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilities_01a01003-ca2a-7bb1-83c8-192f1648e31a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a01003-ca2a-7819-b317-ce0f8bf3391a" xlink:to="loc_us-gaap_DerivativeLiabilities_01a01003-ca2a-7bb1-83c8-192f1648e31a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityStatementOfFinancialPositionExtensibleEnumeration_01a01003-ca2a-795e-8c88-f87e23b5665c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLiabilityStatementOfFinancialPositionExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a01003-ca2a-7819-b317-ce0f8bf3391a" xlink:to="loc_us-gaap_DerivativeLiabilityStatementOfFinancialPositionExtensibleEnumeration_01a01003-ca2a-795e-8c88-f87e23b5665c" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/DERIVATIVESScheduleofEffectofDerivativeInstrumentsDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#DERIVATIVESScheduleofEffectofDerivativeInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/DERIVATIVESScheduleofEffectofDerivativeInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_01a01003-cada-717e-8343-efa99deea9e7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_01a01003-ca2a-7d5b-b572-04c3449ceafe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_01a01003-cada-717e-8343-efa99deea9e7" xlink:to="loc_us-gaap_DerivativeTable_01a01003-ca2a-7d5b-b572-04c3449ceafe" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_01a01003-ca2a-72d7-bf77-e04b8843f611" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a01003-ca2a-7d5b-b572-04c3449ceafe" xlink:to="loc_us-gaap_HedgingDesignationAxis_01a01003-ca2a-72d7-bf77-e04b8843f611" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a01003-ca2a-72d7-bf77-e04b8843f611_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a01003-ca2a-72d7-bf77-e04b8843f611" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a01003-ca2a-72d7-bf77-e04b8843f611_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_01a01003-ca2a-7d54-9f39-8b941336a95f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_01a01003-ca2a-72d7-bf77-e04b8843f611" xlink:to="loc_us-gaap_HedgingDesignationDomain_01a01003-ca2a-7d54-9f39-8b941336a95f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_01a01003-ca2a-7ed7-87f4-e06dd2dc0777" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_01a01003-ca2a-7d54-9f39-8b941336a95f" xlink:to="loc_us-gaap_NondesignatedMember_01a01003-ca2a-7ed7-87f4-e06dd2dc0777" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a01003-ca2a-7474-99ea-9b3e40e7dbd1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a01003-ca2a-7d5b-b572-04c3449ceafe" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a01003-ca2a-7474-99ea-9b3e40e7dbd1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a01003-ca2a-7474-99ea-9b3e40e7dbd1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a01003-ca2a-7474-99ea-9b3e40e7dbd1" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a01003-ca2a-7474-99ea-9b3e40e7dbd1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a01003-ca2a-7b7d-8df5-4a5ada0269cf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a01003-ca2a-7474-99ea-9b3e40e7dbd1" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a01003-ca2a-7b7d-8df5-4a5ada0269cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetsPledgedAsCollateralMember_01a01003-ca2a-771c-a3a1-6eee6996605a" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetsPledgedAsCollateralMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a01003-ca2a-7b7d-8df5-4a5ada0269cf" xlink:to="loc_dfdv_DigitalAssetsPledgedAsCollateralMember_01a01003-ca2a-771c-a3a1-6eee6996605a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetFinancingArrangementsMember_01a01003-ca2a-76b3-8c81-8ec6de6ca5f0" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetFinancingArrangementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a01003-ca2a-7b7d-8df5-4a5ada0269cf" xlink:to="loc_dfdv_DigitalAssetFinancingArrangementsMember_01a01003-ca2a-76b3-8c81-8ec6de6ca5f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetsOtherMember_01a19a3d-70d7-7f82-ba01-13e154268285" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetsOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a01003-ca2a-7b7d-8df5-4a5ada0269cf" xlink:to="loc_dfdv_DigitalAssetsOtherMember_01a19a3d-70d7-7f82-ba01-13e154268285" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_01a01003-cada-7a3b-8397-fa76101d2ddf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a01003-cada-717e-8343-efa99deea9e7" xlink:to="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_01a01003-cada-7a3b-8397-fa76101d2ddf" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/DERIVATIVESAdditionalInformationDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#DERIVATIVESAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/DERIVATIVESAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_01a185f8-5a49-74df-8d73-ee63eb570627" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_01a01003-cada-79fd-b497-c03b75303818" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_01a185f8-5a49-74df-8d73-ee63eb570627" xlink:to="loc_us-gaap_DerivativeTable_01a01003-cada-79fd-b497-c03b75303818" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a185f8-5a49-778c-9a4a-c98d04317379" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a01003-cada-79fd-b497-c03b75303818" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a185f8-5a49-778c-9a4a-c98d04317379" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a185f8-5a49-778c-9a4a-c98d04317379_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a185f8-5a49-778c-9a4a-c98d04317379" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a185f8-5a49-778c-9a4a-c98d04317379_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a185f8-5a49-74a2-94c6-62099470dd5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a185f8-5a49-778c-9a4a-c98d04317379" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a185f8-5a49-74a2-94c6-62099470dd5b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetFinancingArrangementsMember_01a185f8-5a49-7353-a08d-840ab72b40d1" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetFinancingArrangementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a185f8-5a49-74a2-94c6-62099470dd5b" xlink:to="loc_dfdv_DigitalAssetFinancingArrangementsMember_01a185f8-5a49-7353-a08d-840ab72b40d1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_01a185f8-5a49-7a2e-a61d-252276f182ff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a01003-cada-79fd-b497-c03b75303818" xlink:to="loc_us-gaap_TypeOfArrangementAxis_01a185f8-5a49-7a2e-a61d-252276f182ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_01a185f8-5a49-7a2e-a61d-252276f182ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_01a185f8-5a49-7a2e-a61d-252276f182ff" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_01a185f8-5a49-7a2e-a61d-252276f182ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_01a185f8-5a49-7eac-8f01-f58e5c8c21de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_01a185f8-5a49-7a2e-a61d-252276f182ff" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_01a185f8-5a49-7eac-8f01-f58e5c8c21de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_MasterLoanAgreementMember_01a185f8-5a49-7cbb-96cb-680f5a01ac6f" xlink:href="dfdv-20260930.xsd#dfdv_MasterLoanAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_01a185f8-5a49-7eac-8f01-f58e5c8c21de" xlink:to="loc_dfdv_MasterLoanAgreementMember_01a185f8-5a49-7cbb-96cb-680f5a01ac6f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a185f8-5a49-7a7e-b39d-677264c6c03a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a01003-cada-79fd-b497-c03b75303818" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a185f8-5a49-7a7e-b39d-677264c6c03a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a185f8-5a49-7a7e-b39d-677264c6c03a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a185f8-5a49-7a7e-b39d-677264c6c03a" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a185f8-5a49-7a7e-b39d-677264c6c03a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a185f8-5a49-7395-99d7-691ab360d0a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a185f8-5a49-7a7e-b39d-677264c6c03a" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a185f8-5a49-7395-99d7-691ab360d0a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_CollateralizedFinancingArrangementsMember_01a185f8-5a49-7fda-ba27-298339874147" xlink:href="dfdv-20260930.xsd#dfdv_CollateralizedFinancingArrangementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a185f8-5a49-7395-99d7-691ab360d0a9" xlink:to="loc_dfdv_CollateralizedFinancingArrangementsMember_01a185f8-5a49-7fda-ba27-298339874147" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTerm_01a185f8-5a49-79ec-ac7b-71dc45852f0a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a185f8-5a49-74df-8d73-ee63eb570627" xlink:to="loc_us-gaap_DebtInstrumentTerm_01a185f8-5a49-79ec-ac7b-71dc45852f0a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DebtInstrumentRenewalTerm_01a185f8-5a49-79ca-9a79-c501c0d0a015" xlink:href="dfdv-20260930.xsd#dfdv_DebtInstrumentRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a185f8-5a49-74df-8d73-ee63eb570627" xlink:to="loc_dfdv_DebtInstrumentRenewalTerm_01a185f8-5a49-79ca-9a79-c501c0d0a015" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfShortTermDebt_01a185f8-5a49-7888-a8a6-740ddb3353e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfShortTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a185f8-5a49-74df-8d73-ee63eb570627" xlink:to="loc_us-gaap_RepaymentsOfShortTermDebt_01a185f8-5a49-7888-a8a6-740ddb3353e1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBorrowings_01a185f8-5a49-7a34-b882-fd64a8ed61f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a185f8-5a49-74df-8d73-ee63eb570627" xlink:to="loc_us-gaap_ShortTermBorrowings_01a185f8-5a49-7a34-b882-fd64a8ed61f7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseBorrowings_01a185f8-5a49-746c-83e4-cfe0e1722ee1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestExpenseBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a185f8-5a49-74df-8d73-ee63eb570627" xlink:to="loc_us-gaap_InterestExpenseBorrowings_01a185f8-5a49-746c-83e4-cfe0e1722ee1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_ProceedsFromCollateralizedBorrowings_01a185f8-5a49-75bc-b30f-778bd1af08eb" xlink:href="dfdv-20260930.xsd#dfdv_ProceedsFromCollateralizedBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a185f8-5a49-74df-8d73-ee63eb570627" xlink:to="loc_dfdv_ProceedsFromCollateralizedBorrowings_01a185f8-5a49-75bc-b30f-778bd1af08eb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_RepaymentOfCollateralizedBorrowings_01a185f8-5a49-7f89-8df0-417ee3dedc97" xlink:href="dfdv-20260930.xsd#dfdv_RepaymentOfCollateralizedBorrowings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a185f8-5a49-74df-8d73-ee63eb570627" xlink:to="loc_dfdv_RepaymentOfCollateralizedBorrowings_01a185f8-5a49-7f89-8df0-417ee3dedc97" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCollateralAmount_01a185f8-5a49-741a-ba96-96ef061f710c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCollateralAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a185f8-5a49-74df-8d73-ee63eb570627" xlink:to="loc_us-gaap_DebtInstrumentCollateralAmount_01a185f8-5a49-741a-ba96-96ef061f710c" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/DERIVATIVESScheduleofCollateralizedFinancingArrangementsDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#DERIVATIVESScheduleofCollateralizedFinancingArrangementsDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/DERIVATIVESScheduleofCollateralizedFinancingArrangementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_01a01003-cada-7070-9a2a-3d9da71e1eb0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_01a01003-cada-7ab1-93bd-2259864c3921" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_01a01003-cada-7070-9a2a-3d9da71e1eb0" xlink:to="loc_us-gaap_DerivativeTable_01a01003-cada-7ab1-93bd-2259864c3921" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_01a01003-cada-7dfa-9ac9-f95012974f72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a01003-cada-7ab1-93bd-2259864c3921" xlink:to="loc_us-gaap_DebtInstrumentAxis_01a01003-cada-7dfa-9ac9-f95012974f72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a01003-cada-7dfa-9ac9-f95012974f72_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a01003-cada-7dfa-9ac9-f95012974f72" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a01003-cada-7dfa-9ac9-f95012974f72_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_01a01003-cada-714c-87f1-1551e0553fbe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_01a01003-cada-7dfa-9ac9-f95012974f72" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_01a01003-cada-714c-87f1-1551e0553fbe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_CollateralizedFinancingArrangementsMember_01a01003-cada-78a8-9123-75e5e51027ac" xlink:href="dfdv-20260930.xsd#dfdv_CollateralizedFinancingArrangementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_01a01003-cada-714c-87f1-1551e0553fbe" xlink:to="loc_dfdv_CollateralizedFinancingArrangementsMember_01a01003-cada-78a8-9123-75e5e51027ac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_01a01003-cada-71f6-ab7a-228f492629d3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_01a01003-cada-7ab1-93bd-2259864c3921" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_01a01003-cada-71f6-ab7a-228f492629d3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a01003-cada-71f6-ab7a-228f492629d3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a01003-cada-71f6-ab7a-228f492629d3" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a01003-cada-71f6-ab7a-228f492629d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_01a01003-cada-7a7e-a4cb-5d4cfb9e00ee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_01a01003-cada-71f6-ab7a-228f492629d3" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_01a01003-cada-7a7e-a4cb-5d4cfb9e00ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_SolanaSOLMember_01a01003-cada-7fc4-9032-25f41db1f5e6" xlink:href="dfdv-20260930.xsd#dfdv_SolanaSOLMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a01003-cada-7a7e-a4cb-5d4cfb9e00ee" xlink:to="loc_dfdv_SolanaSOLMember_01a01003-cada-7fc4-9032-25f41db1f5e6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_PayPalUSDMember_01a01003-cada-7789-9097-2f2ee31a4294" xlink:href="dfdv-20260930.xsd#dfdv_PayPalUSDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a01003-cada-7a7e-a4cb-5d4cfb9e00ee" xlink:to="loc_dfdv_PayPalUSDMember_01a01003-cada-7789-9097-2f2ee31a4294" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherTradingMember_01a01003-cada-7265-a8d3-021036fd5b0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherTradingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_01a01003-cada-7a7e-a4cb-5d4cfb9e00ee" xlink:to="loc_us-gaap_OtherTradingMember_01a01003-cada-7265-a8d3-021036fd5b0d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollateralAlreadyPostedAggregateFairValue_01a01003-cada-7b01-8977-1301509215d0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollateralAlreadyPostedAggregateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_01a01003-cada-7070-9a2a-3d9da71e1eb0" xlink:to="loc_us-gaap_CollateralAlreadyPostedAggregateFairValue_01a01003-cada-7b01-8977-1301509215d0" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/REDEEMABLEPREFERREDSTOCKNarrativeDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#REDEEMABLEPREFERREDSTOCKNarrativeDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/REDEEMABLEPREFERREDSTOCKNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityByClassOfStockTable_01a16287-c047-7bd4-8ca6-f15504dc19f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityByClassOfStockTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:to="loc_us-gaap_TemporaryEquityByClassOfStockTable_01a16287-c047-7bd4-8ca6-f15504dc19f8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_01a1afa0-8c6a-75d7-b859-5e95b9fb0c8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_01a16287-c047-7bd4-8ca6-f15504dc19f8" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_01a1afa0-8c6a-75d7-b859-5e95b9fb0c8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a1afa0-8c6a-75d7-b859-5e95b9fb0c8e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_01a1afa0-8c6a-75d7-b859-5e95b9fb0c8e" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a1afa0-8c6a-75d7-b859-5e95b9fb0c8e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a1afa0-8c6a-78f0-ac56-0d0df506c115" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_01a1afa0-8c6a-75d7-b859-5e95b9fb0c8e" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a1afa0-8c6a-78f0-ac56-0d0df506c115" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_PublicStockOfferingMember_01a1afa0-8c6a-7650-a6dc-6c2d09b768b4" xlink:href="dfdv-20260930.xsd#dfdv_PublicStockOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a1afa0-8c6a-78f0-ac56-0d0df506c115" xlink:to="loc_dfdv_PublicStockOfferingMember_01a1afa0-8c6a-7650-a6dc-6c2d09b768b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OverAllotmentOptionMember_01a1c11c-7442-7e1c-bf05-d21e311523db" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OverAllotmentOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a1afa0-8c6a-78f0-ac56-0d0df506c115" xlink:to="loc_us-gaap_OverAllotmentOptionMember_01a1c11c-7442-7e1c-bf05-d21e311523db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_AtTheMarketOfferingMember_01a1c11e-ace6-75b2-a66a-7275bd20f4dc" xlink:href="dfdv-20260930.xsd#dfdv_AtTheMarketOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a1afa0-8c6a-78f0-ac56-0d0df506c115" xlink:to="loc_dfdv_AtTheMarketOfferingMember_01a1c11e-ace6-75b2-a66a-7275bd20f4dc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_01a1afa0-c4b7-7594-bb36-5302ba43e20d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_01a16287-c047-7bd4-8ca6-f15504dc19f8" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_01a1afa0-c4b7-7594-bb36-5302ba43e20d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_01a1afa0-c4b7-7594-bb36-5302ba43e20d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_01a1afa0-c4b7-7594-bb36-5302ba43e20d" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_01a1afa0-c4b7-7594-bb36-5302ba43e20d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_01a1afa0-c4b7-7a76-b233-41ae51d2573e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_01a1afa0-c4b7-7594-bb36-5302ba43e20d" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_01a1afa0-c4b7-7a76-b233-41ae51d2573e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_01a1afa0-c4b7-7236-ab5a-f79dfca3a16b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_01a1afa0-c4b7-7a76-b233-41ae51d2573e" xlink:to="loc_us-gaap_SubsequentEventMember_01a1afa0-c4b7-7236-ab5a-f79dfca3a16b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_01a1b2a4-3c5a-7bcb-bd30-3233cd09e9f1" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_01a16287-c047-7bd4-8ca6-f15504dc19f8" xlink:to="loc_srt_RangeAxis_01a1b2a4-3c5a-7bcb-bd30-3233cd09e9f1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a1b2a4-3c5a-7bcb-bd30-3233cd09e9f1_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_01a1b2a4-3c5a-7bcb-bd30-3233cd09e9f1" xlink:to="loc_srt_RangeMember_01a1b2a4-3c5a-7bcb-bd30-3233cd09e9f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_01a1b2a4-3c5a-7255-966b-2edded5f1952" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_01a1b2a4-3c5a-7bcb-bd30-3233cd09e9f1" xlink:to="loc_srt_RangeMember_01a1b2a4-3c5a-7255-966b-2edded5f1952" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_01a1b2a4-3c5a-7e37-894a-fbeab23335f2" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a1b2a4-3c5a-7255-966b-2edded5f1952" xlink:to="loc_srt_MaximumMember_01a1b2a4-3c5a-7e37-894a-fbeab23335f2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_01a1b2a4-5333-74f4-a015-d2ae6f43061a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_01a1b2a4-3c5a-7255-966b-2edded5f1952" xlink:to="loc_srt_MinimumMember_01a1b2a4-5333-74f4-a015-d2ae6f43061a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_01a1c11b-80e1-7b75-aa8a-2d030d1380e2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_TemporaryEquityByClassOfStockTable_01a16287-c047-7bd4-8ca6-f15504dc19f8" xlink:to="loc_us-gaap_StatementClassOfStockAxis_01a1c11b-80e1-7b75-aa8a-2d030d1380e2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a1c11b-80e1-7b75-aa8a-2d030d1380e2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a1c11b-80e1-7b75-aa8a-2d030d1380e2" xlink:to="loc_us-gaap_ClassOfStockDomain_01a1c11b-80e1-7b75-aa8a-2d030d1380e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a1c11b-80e1-7b48-94fb-a3e954507364" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a1c11b-80e1-7b75-aa8a-2d030d1380e2" xlink:to="loc_us-gaap_ClassOfStockDomain_01a1c11b-80e1-7b48-94fb-a3e954507364" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemablePreferredStockMember_01a1c11b-be5c-76d0-8f14-eff71c867193" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RedeemablePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a1c11b-80e1-7b48-94fb-a3e954507364" xlink:to="loc_us-gaap_RedeemablePreferredStockMember_01a1c11b-be5c-76d0-8f14-eff71c867193" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_01a1afa0-8c6a-7e84-9e2e-02ef1b08c88f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_01a1afa0-8c6a-7e84-9e2e-02ef1b08c88f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_TemporaryEquityParValuePerShare_01a1c11a-e127-7fc4-a705-52d7128c5485" xlink:href="dfdv-20260930.xsd#dfdv_TemporaryEquityParValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:to="loc_dfdv_TemporaryEquityParValuePerShare_01a1c11a-e127-7fc4-a705-52d7128c5485" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockPricePerShare_01a1c11b-689c-717f-be44-0a700aa7c03d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:to="loc_us-gaap_SaleOfStockPricePerShare_01a1c11b-689c-717f-be44-0a700aa7c03d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfRedeemablePreferredStock_01a1afa0-8c6a-7aa9-b364-50d1f3be6266" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfRedeemablePreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfRedeemablePreferredStock_01a1afa0-8c6a-7aa9-b364-50d1f3be6266" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues_01a1afa0-8c6a-7c4f-857e-0f3b1ceeb630" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:to="loc_us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues_01a1afa0-8c6a-7c4f-857e-0f3b1ceeb630" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_SaleOfStockPurchaseOptionTerm_01a1afa0-c4b8-7a9a-9a93-437fb6e905c3" xlink:href="dfdv-20260930.xsd#dfdv_SaleOfStockPurchaseOptionTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:to="loc_dfdv_SaleOfStockPurchaseOptionTerm_01a1afa0-c4b8-7a9a-9a93-437fb6e905c3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_SaleOfStockMaximumAuthorizedShares_01a1c11d-f8bb-724d-9aba-e22b56685491" xlink:href="dfdv-20260930.xsd#dfdv_SaleOfStockMaximumAuthorizedShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:to="loc_dfdv_SaleOfStockMaximumAuthorizedShares_01a1c11d-f8bb-724d-9aba-e22b56685491" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_TemporaryEquityStatedValuePerShare_01a1c11f-282d-7001-ba4c-2a15cb891e3e" xlink:href="dfdv-20260930.xsd#dfdv_TemporaryEquityStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:to="loc_dfdv_TemporaryEquityStatedValuePerShare_01a1c11f-282d-7001-ba4c-2a15cb891e3e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityLiquidationPreferencePerShare_01a1afa0-c4b8-7f08-abea-84f41d43955c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityLiquidationPreferencePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:to="loc_us-gaap_TemporaryEquityLiquidationPreferencePerShare_01a1afa0-c4b8-7f08-abea-84f41d43955c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_TemporaryEquityDividendRatePerDollarAmount_01a1afa0-c4b8-706b-8f63-2876187e7422" xlink:href="dfdv-20260930.xsd#dfdv_TemporaryEquityDividendRatePerDollarAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:to="loc_dfdv_TemporaryEquityDividendRatePerDollarAmount_01a1afa0-c4b8-706b-8f63-2876187e7422" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_TemporaryEquityDividendRatePercentage_01a1afa0-c4b8-7920-90d4-68b2950b3cba" xlink:href="dfdv-20260930.xsd#dfdv_TemporaryEquityDividendRatePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:to="loc_dfdv_TemporaryEquityDividendRatePercentage_01a1afa0-c4b8-7920-90d4-68b2950b3cba" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_TemporaryEquityDividendReserve_01a1afa0-c4b8-7961-bd9f-fc68b658a343" xlink:href="dfdv-20260930.xsd#dfdv_TemporaryEquityDividendReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:to="loc_dfdv_TemporaryEquityDividendReserve_01a1afa0-c4b8-7961-bd9f-fc68b658a343" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityRedemptionPricePerShare_01a1afa0-c4b8-7699-ab29-206a92b248cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityRedemptionPricePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:to="loc_us-gaap_TemporaryEquityRedemptionPricePerShare_01a1afa0-c4b8-7699-ab29-206a92b248cb" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_TemporaryEquityRedemptionPricePerShareUponFundamentalChange_01a1c11f-ea27-7614-891f-ac4952376620" xlink:href="dfdv-20260930.xsd#dfdv_TemporaryEquityRedemptionPricePerShareUponFundamentalChange"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:to="loc_dfdv_TemporaryEquityRedemptionPricePerShareUponFundamentalChange_01a1c11f-ea27-7614-891f-ac4952376620" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_TemporaryEquityFundamentalChangeRedemptionRepurchasePeriod_01a1afa0-c4b8-71fa-ac78-dbd1386bfb0e" xlink:href="dfdv-20260930.xsd#dfdv_TemporaryEquityFundamentalChangeRedemptionRepurchasePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_01a1afa0-8c6a-7f72-b810-48e0801c86e1" xlink:to="loc_dfdv_TemporaryEquityFundamentalChangeRedemptionRepurchasePeriod_01a1afa0-c4b8-71fa-ac78-dbd1386bfb0e" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/STOCKHOLDERSEQUITYAdditionalInformationDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#STOCKHOLDERSEQUITYAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/STOCKHOLDERSEQUITYAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_01a01003-cada-7ea0-a2ff-26344d6edf94" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_01a01003-cada-7ea0-a2ff-26344d6edf94" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_01a01003-cada-733e-b9ec-cb131c372988" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_01a01003-cada-7ea0-a2ff-26344d6edf94" xlink:to="loc_us-gaap_StatementClassOfStockAxis_01a01003-cada-733e-b9ec-cb131c372988" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a01003-cada-733e-b9ec-cb131c372988_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a01003-cada-733e-b9ec-cb131c372988" xlink:to="loc_us-gaap_ClassOfStockDomain_01a01003-cada-733e-b9ec-cb131c372988_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a01003-cada-7d2c-9e1b-959d6654a36a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a01003-cada-733e-b9ec-cb131c372988" xlink:to="loc_us-gaap_ClassOfStockDomain_01a01003-cada-7d2c-9e1b-959d6654a36a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_OneSeriesDetachableStockWarrantMember_01a01003-cada-784e-b625-d65871f49bbd" xlink:href="dfdv-20260930.xsd#dfdv_OneSeriesDetachableStockWarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a01003-cada-7d2c-9e1b-959d6654a36a" xlink:to="loc_dfdv_OneSeriesDetachableStockWarrantMember_01a01003-cada-784e-b625-d65871f49bbd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_TwoSeriesOfDetachableStockWarrantMember_01a01003-cada-74af-b5a5-1061a11f6085" xlink:href="dfdv-20260930.xsd#dfdv_TwoSeriesOfDetachableStockWarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a01003-cada-7d2c-9e1b-959d6654a36a" xlink:to="loc_dfdv_TwoSeriesOfDetachableStockWarrantMember_01a01003-cada-74af-b5a5-1061a11f6085" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01a01003-cada-73b5-aeb4-d301cf4cf267" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_01a01003-cada-7ea0-a2ff-26344d6edf94" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01a01003-cada-73b5-aeb4-d301cf4cf267" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a01003-cada-73b5-aeb4-d301cf4cf267_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a01003-cada-73b5-aeb4-d301cf4cf267" xlink:to="loc_us-gaap_EquityComponentDomain_01a01003-cada-73b5-aeb4-d301cf4cf267_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a01003-cada-7f7e-a497-9a5bbbef0688" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a01003-cada-73b5-aeb4-d301cf4cf267" xlink:to="loc_us-gaap_EquityComponentDomain_01a01003-cada-7f7e-a497-9a5bbbef0688" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_01a01003-cada-759c-a183-6721e79bdc0f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a01003-cada-7f7e-a497-9a5bbbef0688" xlink:to="loc_us-gaap_CommonStockMember_01a01003-cada-759c-a183-6721e79bdc0f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeAxis_01a01003-cada-7b66-85d2-3fd6e0fa0e39" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_01a01003-cada-7ea0-a2ff-26344d6edf94" xlink:to="loc_us-gaap_ShortTermDebtTypeAxis_01a01003-cada-7b66-85d2-3fd6e0fa0e39" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_01a01003-cada-7b66-85d2-3fd6e0fa0e39_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_01a01003-cada-7b66-85d2-3fd6e0fa0e39" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_01a01003-cada-7b66-85d2-3fd6e0fa0e39_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermDebtTypeDomain_01a01003-cada-715b-8168-5dc254ecb3e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShortTermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShortTermDebtTypeAxis_01a01003-cada-7b66-85d2-3fd6e0fa0e39" xlink:to="loc_us-gaap_ShortTermDebtTypeDomain_01a01003-cada-715b-8168-5dc254ecb3e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleNotesPayableMember_01a01003-cada-75ba-bc1c-8c4b411255d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConvertibleNotesPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermDebtTypeDomain_01a01003-cada-715b-8168-5dc254ecb3e4" xlink:to="loc_us-gaap_ConvertibleNotesPayableMember_01a01003-cada-75ba-bc1c-8c4b411255d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_01a01003-cada-7593-848a-384dde23e661" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_01a01003-cada-7ea0-a2ff-26344d6edf94" xlink:to="loc_us-gaap_TypeOfArrangementAxis_01a01003-cada-7593-848a-384dde23e661" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_01a01003-cada-7593-848a-384dde23e661_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_01a01003-cada-7593-848a-384dde23e661" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_01a01003-cada-7593-848a-384dde23e661_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_01a01003-cada-722e-bb27-0a64cd6ae894" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_01a01003-cada-7593-848a-384dde23e661" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_01a01003-cada-722e-bb27-0a64cd6ae894" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_SecuritiesPurchaseAgreementMember_01a01003-cada-7cb9-a31e-652db9092335" xlink:href="dfdv-20260930.xsd#dfdv_SecuritiesPurchaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_01a01003-cada-722e-bb27-0a64cd6ae894" xlink:to="loc_dfdv_SecuritiesPurchaseAgreementMember_01a01003-cada-7cb9-a31e-652db9092335" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_01a01003-cada-7ede-abba-5eead13ca6c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_01a01003-cada-7ea0-a2ff-26344d6edf94" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_01a01003-cada-7ede-abba-5eead13ca6c7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a01003-cada-7ede-abba-5eead13ca6c7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a01003-cada-7ede-abba-5eead13ca6c7" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a01003-cada-7ede-abba-5eead13ca6c7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a01003-cada-7c6a-ba30-dad72d0edcb2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a01003-cada-7ede-abba-5eead13ca6c7" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a01003-cada-7c6a-ba30-dad72d0edcb2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_WarrantDividendMember_01a01003-cada-7fb2-81ed-79f21ab530c3" xlink:href="dfdv-20260930.xsd#dfdv_WarrantDividendMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a01003-cada-7c6a-ba30-dad72d0edcb2" xlink:to="loc_dfdv_WarrantDividendMember_01a01003-cada-7fb2-81ed-79f21ab530c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_PreFundedWarrantsMember_01a01003-cada-7ced-9775-ee6f2d07c0c2" xlink:href="dfdv-20260930.xsd#dfdv_PreFundedWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a01003-cada-7c6a-ba30-dad72d0edcb2" xlink:to="loc_dfdv_PreFundedWarrantsMember_01a01003-cada-7ced-9775-ee6f2d07c0c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_01a01003-cada-7272-8e01-4bde48db5ad4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_01a01003-cada-7ea0-a2ff-26344d6edf94" xlink:to="loc_us-gaap_CreditFacilityAxis_01a01003-cada-7272-8e01-4bde48db5ad4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a01003-cada-7272-8e01-4bde48db5ad4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_01a01003-cada-7272-8e01-4bde48db5ad4" xlink:to="loc_us-gaap_CreditFacilityDomain_01a01003-cada-7272-8e01-4bde48db5ad4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a01003-cada-74c1-b6b1-93f38e337547" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_01a01003-cada-7272-8e01-4bde48db5ad4" xlink:to="loc_us-gaap_CreditFacilityDomain_01a01003-cada-74c1-b6b1-93f38e337547" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_01a01003-cada-7e2d-8433-8d65f28756d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_01a01003-cada-74c1-b6b1-93f38e337547" xlink:to="loc_us-gaap_LineOfCreditMember_01a01003-cada-7e2d-8433-8d65f28756d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsAxis_01a01003-cada-792a-ac28-14c8338382c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCommitmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_01a01003-cada-7ea0-a2ff-26344d6edf94" xlink:to="loc_us-gaap_OtherCommitmentsAxis_01a01003-cada-792a-ac28-14c8338382c2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsDomain_01a01003-cada-792a-ac28-14c8338382c2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCommitmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_OtherCommitmentsAxis_01a01003-cada-792a-ac28-14c8338382c2" xlink:to="loc_us-gaap_OtherCommitmentsDomain_01a01003-cada-792a-ac28-14c8338382c2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsDomain_01a01003-cada-7796-9df9-7bbcbbb1ea10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCommitmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_OtherCommitmentsAxis_01a01003-cada-792a-ac28-14c8338382c2" xlink:to="loc_us-gaap_OtherCommitmentsDomain_01a01003-cada-7796-9df9-7bbcbbb1ea10" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_InvestmentAndOtherNonoperatingIncomeExpenseMember_01a01003-cada-7dc3-b430-33d34e1a3e01" xlink:href="dfdv-20260930.xsd#dfdv_InvestmentAndOtherNonoperatingIncomeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsDomain_01a01003-cada-7796-9df9-7bbcbbb1ea10" xlink:to="loc_dfdv_InvestmentAndOtherNonoperatingIncomeExpenseMember_01a01003-cada-7dc3-b430-33d34e1a3e01" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMember_01a01003-cada-7762-8014-831f49b4abe1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsDomain_01a01003-cada-7796-9df9-7bbcbbb1ea10" xlink:to="loc_us-gaap_EquityMember_01a01003-cada-7762-8014-831f49b4abe1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_01a01003-cada-7835-9bb6-886e0fb748be" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_01a01003-cada-7ea0-a2ff-26344d6edf94" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_01a01003-cada-7835-9bb6-886e0fb748be" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a01003-cada-7835-9bb6-886e0fb748be_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_01a01003-cada-7835-9bb6-886e0fb748be" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a01003-cada-7835-9bb6-886e0fb748be_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a01003-cada-7845-baa1-f8bdd94f0fb3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_01a01003-cada-7835-9bb6-886e0fb748be" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a01003-cada-7845-baa1-f8bdd94f0fb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_AtTheMarketOfferingMember_01a01003-cada-7e75-a537-ff4b7fb4795d" xlink:href="dfdv-20260930.xsd#dfdv_AtTheMarketOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a01003-cada-7845-baa1-f8bdd94f0fb3" xlink:to="loc_dfdv_AtTheMarketOfferingMember_01a01003-cada-7e75-a537-ff4b7fb4795d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_01a01003-cada-776d-bf51-620eec68d4c7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_01a01003-cada-776d-bf51-620eec68d4c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_01a01003-cada-70a8-878d-43e05e4d90c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_01a01003-cada-70a8-878d-43e05e4d90c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_ClassOfWarrantOrRightNumberOfWarrantSeriesIssued_01a01003-cada-7211-af54-3d45693c3704" xlink:href="dfdv-20260930.xsd#dfdv_ClassOfWarrantOrRightNumberOfWarrantSeriesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_dfdv_ClassOfWarrantOrRightNumberOfWarrantSeriesIssued_01a01003-cada-7211-af54-3d45693c3704" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_01a1c657-4d02-717a-9260-8383c5b0acc6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentConvertibleConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_01a1c657-4d02-717a-9260-8383c5b0acc6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_01a01003-cada-70a7-83f7-a368bee1b84a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_01a01003-cada-70a7-83f7-a368bee1b84a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight_01a01003-cada-7ad7-977b-9d6f2fcd2c38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight_01a01003-cada-7ad7-977b-9d6f2fcd2c38" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_01a01003-cada-7b96-aee5-4b4a7dbe6e75" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_01a01003-cada-7b96-aee5-4b4a7dbe6e75" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_01a01003-cada-718e-bfd4-092f2b5c7403" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_01a01003-cada-718e-bfd4-092f2b5c7403" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_WarrantDividendFairValue_01a01003-cada-779b-9a38-f6b95cd0c56c" xlink:href="dfdv-20260930.xsd#dfdv_WarrantDividendFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_dfdv_WarrantDividendFairValue_01a01003-cada-779b-9a38-f6b95cd0c56c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingTerm_01a01003-cada-7360-93a5-6045472d3e38" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstandingTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingTerm_01a01003-cada-7360-93a5-6045472d3e38" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_01a01003-cada-7b56-8c0e-60902929d6bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_01a01003-cada-7b56-8c0e-60902929d6bb" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_NumberOfPurchaseCommonStock_01a01003-cada-73d0-b4ec-3a02daa62fd8" xlink:href="dfdv-20260930.xsd#dfdv_NumberOfPurchaseCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_dfdv_NumberOfPurchaseCommonStock_01a01003-cada-73d0-b4ec-3a02daa62fd8" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharePrice_01a01003-cada-767c-b5f5-b505c554e748" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_SharePrice_01a01003-cada-767c-b5f5-b505c554e748" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_StockIssuedDuringPeriodValueWarrantsExercised_01a01003-cada-7a47-94de-e28e56c0e225" xlink:href="dfdv-20260930.xsd#dfdv_StockIssuedDuringPeriodValueWarrantsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_dfdv_StockIssuedDuringPeriodValueWarrantsExercised_01a01003-cada-7a47-94de-e28e56c0e225" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_01a01003-cada-743f-8679-78be5cf24fb9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_01a01003-cada-743f-8679-78be5cf24fb9" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfPrivatePlacement_01a01003-cada-729d-a2c0-6a5fc1d01941" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfPrivatePlacement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfPrivatePlacement_01a01003-cada-729d-a2c0-6a5fc1d01941" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_ClassOfWarrantOrRightExercisablePeriod_01a01003-cada-7d0a-9c97-281595e519a0" xlink:href="dfdv-20260930.xsd#dfdv_ClassOfWarrantOrRightExercisablePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_dfdv_ClassOfWarrantOrRightExercisablePeriod_01a01003-cada-7d0a-9c97-281595e519a0" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_NumberOfWarrantsExercised_01a01003-cada-7c4b-ba1f-1601be52bb05" xlink:href="dfdv-20260930.xsd#dfdv_NumberOfWarrantsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_dfdv_NumberOfWarrantsExercised_01a01003-cada-7c4b-ba1f-1601be52bb05" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_01a01003-cada-7fac-9306-f1131ce0cc9b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_01a01003-cada-7fac-9306-f1131ce0cc9b" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_01a01003-cada-7055-bc7b-7dc0b1deb230" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_LineOfCredit_01a01003-cada-7055-bc7b-7dc0b1deb230" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeeAmount_01a01003-cada-7291-8f86-966dd4c75752" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityCommitmentFeeAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeeAmount_01a01003-cada-7291-8f86-966dd4c75752" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_LineOfCreditFacilityCommitmentFeePeriod_01a01003-cada-703d-8c6c-314d50853e67" xlink:href="dfdv-20260930.xsd#dfdv_LineOfCreditFacilityCommitmentFeePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_dfdv_LineOfCreditFacilityCommitmentFeePeriod_01a01003-cada-703d-8c6c-314d50853e67" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_CommonStockIssuanceInConnectionWithEquityLineOfCreditCommitmentFee_01a01003-cada-7c9f-bdec-4c2024c1963f" xlink:href="dfdv-20260930.xsd#dfdv_CommonStockIssuanceInConnectionWithEquityLineOfCreditCommitmentFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_dfdv_CommonStockIssuanceInConnectionWithEquityLineOfCreditCommitmentFee_01a01003-cada-7c9f-bdec-4c2024c1963f" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_SharesIssuedForCommitmentFee_01a01003-cada-799b-be5d-3e3d581420f0" xlink:href="dfdv-20260930.xsd#dfdv_SharesIssuedForCommitmentFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_dfdv_SharesIssuedForCommitmentFee_01a01003-cada-799b-be5d-3e3d581420f0" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_01a01003-cada-7afd-ab49-f2ae55bc895b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_01a01003-cada-7afd-ab49-f2ae55bc895b" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_01a01003-cada-723e-b92f-7688cba752e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_01a01003-cada-723e-b92f-7688cba752e6" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_01a01003-cada-7212-8a9d-253e2295d714" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_01a01003-cada-7212-8a9d-253e2295d714" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedPerTransaction_01a01003-cada-7f94-9245-4da3ba2f03a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockConsiderationReceivedPerTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_01a01003-cada-7c02-a744-e3dcd19a8593" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedPerTransaction_01a01003-cada-7f94-9245-4da3ba2f03a5" xlink:type="arc" order="27"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/STOCKHOLDERSEQUITYScheduleofAccumulatedComprehensiveLossIncomeDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#STOCKHOLDERSEQUITYScheduleofAccumulatedComprehensiveLossIncomeDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/STOCKHOLDERSEQUITYScheduleofAccumulatedComprehensiveLossIncomeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_01a01003-cada-72bd-bc6c-397b7ee5ad64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_01a01003-cada-7862-914d-4b304fad7dce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_01a01003-cada-72bd-bc6c-397b7ee5ad64" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_01a01003-cada-7862-914d-4b304fad7dce" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01a01003-cada-728d-b795-2d6ba647d7b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_01a01003-cada-7862-914d-4b304fad7dce" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01a01003-cada-728d-b795-2d6ba647d7b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a01003-cada-728d-b795-2d6ba647d7b4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a01003-cada-728d-b795-2d6ba647d7b4" xlink:to="loc_us-gaap_EquityComponentDomain_01a01003-cada-728d-b795-2d6ba647d7b4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a01003-cada-71d5-8e6d-55c6eb0012a9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a01003-cada-728d-b795-2d6ba647d7b4" xlink:to="loc_us-gaap_EquityComponentDomain_01a01003-cada-71d5-8e6d-55c6eb0012a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a01003-cada-75ba-8c25-c2f033d65cc3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a01003-cada-71d5-8e6d-55c6eb0012a9" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_01a01003-cada-75ba-8c25-c2f033d65cc3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_01a01003-cada-709e-a1f9-5ed5a48eb816" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AOCIAttributableToParentNetOfTaxRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_01a01003-cada-72bd-bc6c-397b7ee5ad64" xlink:to="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_01a01003-cada-709e-a1f9-5ed5a48eb816" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a01003-cada-70e9-9ada-365a0659273c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_01a01003-cada-709e-a1f9-5ed5a48eb816" xlink:to="loc_us-gaap_StockholdersEquity_01a01003-cada-70e9-9ada-365a0659273c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_01a01003-cada-7184-b065-ccb178f59717" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_01a01003-cada-709e-a1f9-5ed5a48eb816" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_01a01003-cada-7184-b065-ccb178f59717" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_01a01003-cada-7b2e-b88c-5830ea889596" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/SHAREBASEDCOMPENSATIONScheduleofStockBasedCompensationDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#SHAREBASEDCOMPENSATIONScheduleofStockBasedCompensationDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/SHAREBASEDCOMPENSATIONScheduleofStockBasedCompensationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-7246-9a29-dc15099d065c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a01003-cada-78ca-898d-8e0fda326d4d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-7246-9a29-dc15099d065c" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a01003-cada-78ca-898d-8e0fda326d4d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_01a01003-cada-7b7d-8c85-d8d3cd370478" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfIncomeLocationBalanceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a01003-cada-78ca-898d-8e0fda326d4d" xlink:to="loc_us-gaap_StatementOfIncomeLocationBalanceAxis_01a01003-cada-7b7d-8c85-d8d3cd370478" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a01003-cada-704f-95d7-b65cba365001" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-7246-9a29-dc15099d065c" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a01003-cada-704f-95d7-b65cba365001" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/SHAREBASEDCOMPENSATIONScheduleofStockBasedCompensationDetails_1" xlink:type="simple" xlink:href="dfdv-20260930.xsd#SHAREBASEDCOMPENSATIONScheduleofStockBasedCompensationDetails_1"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/SHAREBASEDCOMPENSATIONScheduleofStockBasedCompensationDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-7246-9a29-dc15099d065c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a01003-cada-78ca-898d-8e0fda326d4d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-7246-9a29-dc15099d065c" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a01003-cada-78ca-898d-8e0fda326d4d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a01003-cada-704f-95d7-b65cba365001" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-7246-9a29-dc15099d065c" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_01a01003-cada-704f-95d7-b65cba365001" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/SHAREBASEDCOMPENSATIONScheduleofInformationRelatedtoStockOptionsDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#SHAREBASEDCOMPENSATIONScheduleofInformationRelatedtoStockOptionsDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/SHAREBASEDCOMPENSATIONScheduleofInformationRelatedtoStockOptionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-78a3-a311-0d33985ccd2d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a01003-cada-7ec6-99f0-28550e4f7e94" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-78a3-a311-0d33985ccd2d" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a01003-cada-7ec6-99f0-28550e4f7e94" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityTypeAxis_01a01003-cada-7db5-8a20-9f499e85675d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OptionIndexedToIssuersEquityTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a01003-cada-7ec6-99f0-28550e4f7e94" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityTypeAxis_01a01003-cada-7db5-8a20-9f499e85675d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_01a01003-cada-7db5-8a20-9f499e85675d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OptionIndexedToIssuersEquityTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityTypeAxis_01a01003-cada-7db5-8a20-9f499e85675d" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_01a01003-cada-7db5-8a20-9f499e85675d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_01a01003-cada-7193-bc45-ab0c8f5b2a89" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OptionIndexedToIssuersEquityTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityTypeAxis_01a01003-cada-7db5-8a20-9f499e85675d" xlink:to="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_01a01003-cada-7193-bc45-ab0c8f5b2a89" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_01a01003-cada-7b0f-bac2-74d6a15b6b03" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OptionIndexedToIssuersEquityTypeDomain_01a01003-cada-7193-bc45-ab0c8f5b2a89" xlink:to="loc_us-gaap_EmployeeStockOptionMember_01a01003-cada-7b0f-bac2-74d6a15b6b03" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_01a01003-cada-726e-8553-d0747e68794f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-78a3-a311-0d33985ccd2d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_01a01003-cada-726e-8553-d0747e68794f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_01a01003-cada-7bee-b1a8-67606329b3ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_01a01003-cada-726e-8553-d0747e68794f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_01a01003-cada-7bee-b1a8-67606329b3ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_01a01003-cada-7089-8f76-471425e66dba" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_01a01003-cada-726e-8553-d0747e68794f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_01a01003-cada-7089-8f76-471425e66dba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_01a01003-cada-726a-8bc4-55a2b3aeb91d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_01a01003-cada-726e-8553-d0747e68794f" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_01a01003-cada-726a-8bc4-55a2b3aeb91d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_01a01003-cada-7368-8a7d-3bc0a96c8c0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_01a01003-cada-726e-8553-d0747e68794f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_01a01003-cada-7368-8a7d-3bc0a96c8c0d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_01a01003-cada-7659-87dd-ce3086da41da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_01a01003-cada-7e18-92b2-9e9cb536531b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-78a3-a311-0d33985ccd2d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_01a01003-cada-7e18-92b2-9e9cb536531b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_01a01003-cada-7368-bfcd-32c736ca87b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_01a01003-cada-7e18-92b2-9e9cb536531b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_01a01003-cada-7368-bfcd-32c736ca87b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_01a01003-cada-7ad3-8ef0-75c39cdd0ad6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_01a01003-cada-7e18-92b2-9e9cb536531b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_01a01003-cada-7ad3-8ef0-75c39cdd0ad6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_01a01003-cada-7034-b173-6f887c9e6f3b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_01a01003-cada-7e18-92b2-9e9cb536531b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_01a01003-cada-7034-b173-6f887c9e6f3b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_01a01003-cada-735b-bb47-d2072c402024" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_01a01003-cada-7e18-92b2-9e9cb536531b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_01a01003-cada-735b-bb47-d2072c402024" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_01a01003-cada-7ce4-bf11-fe142897c38a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_01a01003-cada-7eba-bccb-103d36de7bff" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-78a3-a311-0d33985ccd2d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_01a01003-cada-7eba-bccb-103d36de7bff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_01a01003-cada-7ceb-b511-b46b6ff63881" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_01a01003-cada-7eba-bccb-103d36de7bff" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_01a01003-cada-7ceb-b511-b46b6ff63881" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_01a01003-cada-7c7f-aaf8-d10b9fef3b3a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract_01a01003-cada-7eba-bccb-103d36de7bff" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_01a01003-cada-7c7f-aaf8-d10b9fef3b3a" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/SHAREBASEDCOMPENSATIONAdditionalInformationDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#SHAREBASEDCOMPENSATIONAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/SHAREBASEDCOMPENSATIONAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-7f3a-a0b2-891f52d5a852" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a01003-cada-7338-82a8-9a2e0b4bf9bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-7f3a-a0b2-891f52d5a852" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a01003-cada-7338-82a8-9a2e0b4bf9bf" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a01003-cada-73a7-9438-d836d4bf9589" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a01003-cada-7338-82a8-9a2e0b4bf9bf" xlink:to="loc_us-gaap_AwardTypeAxis_01a01003-cada-73a7-9438-d836d4bf9589" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-cada-73a7-9438-d836d4bf9589_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_01a01003-cada-73a7-9438-d836d4bf9589" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-cada-73a7-9438-d836d4bf9589_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-cada-7b1d-97c4-76593be2ba33" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_01a01003-cada-73a7-9438-d836d4bf9589" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-cada-7b1d-97c4-76593be2ba33" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_01a01003-cada-7543-884c-548b90aac672" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-cada-7b1d-97c4-76593be2ba33" xlink:to="loc_us-gaap_EmployeeStockOptionMember_01a01003-cada-7543-884c-548b90aac672" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_01a01003-cada-733b-8206-515abb4768de" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-cada-7b1d-97c4-76593be2ba33" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_01a01003-cada-733b-8206-515abb4768de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_01a01003-cada-7af6-8fbe-45aa9e3fc889" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-7f3a-a0b2-891f52d5a852" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_01a01003-cada-7af6-8fbe-45aa9e3fc889" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_01a01003-cada-79d1-b8a6-3622b5c9b411" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-7f3a-a0b2-891f52d5a852" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_01a01003-cada-79d1-b8a6-3622b5c9b411" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/SHAREBASEDCOMPENSATIONScheduleofInformationRelatedtoRestrictedStockUnitsDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#SHAREBASEDCOMPENSATIONScheduleofInformationRelatedtoRestrictedStockUnitsDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/SHAREBASEDCOMPENSATIONScheduleofInformationRelatedtoRestrictedStockUnitsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-7f34-b29a-6e5071f2666f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a01003-cada-7b02-a241-506e8a544636" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-7f34-b29a-6e5071f2666f" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a01003-cada-7b02-a241-506e8a544636" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_01a01003-cada-7c7e-9da2-c090caac294d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_01a01003-cada-7b02-a241-506e8a544636" xlink:to="loc_us-gaap_AwardTypeAxis_01a01003-cada-7c7e-9da2-c090caac294d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-cada-7c7e-9da2-c090caac294d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_01a01003-cada-7c7e-9da2-c090caac294d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-cada-7c7e-9da2-c090caac294d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-cada-79aa-ae62-3257240b80d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_01a01003-cada-7c7e-9da2-c090caac294d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-cada-79aa-ae62-3257240b80d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_01a01003-cada-7da0-a49a-607f7f5394bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01a01003-cada-79aa-ae62-3257240b80d6" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_01a01003-cada-7da0-a49a-607f7f5394bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_01a01003-cada-77fa-bf20-e842399f0fe5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-7f34-b29a-6e5071f2666f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_01a01003-cada-77fa-bf20-e842399f0fe5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_01a01003-cada-73a2-b2bc-f544cf51fddc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_01a01003-cada-77fa-bf20-e842399f0fe5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_01a01003-cada-73a2-b2bc-f544cf51fddc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01a01003-cadb-7bb9-9fec-70f3abc8c511" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_01a01003-cada-77fa-bf20-e842399f0fe5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_01a01003-cadb-7bb9-9fec-70f3abc8c511" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_01a01003-cadb-712c-8745-85f4aedf25f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_01a01003-cada-77fa-bf20-e842399f0fe5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_01a01003-cadb-712c-8745-85f4aedf25f8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_01a01003-cadb-7d3f-8fc8-65c8fa600d62" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_01a01003-cadb-70a8-becb-7817b98c76e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_01a01003-cada-7f34-b29a-6e5071f2666f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_01a01003-cadb-70a8-becb-7817b98c76e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_01a01003-cadb-7c6e-ba4f-5a6150526394" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_01a01003-cadb-70a8-becb-7817b98c76e5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_01a01003-cadb-7c6e-ba4f-5a6150526394" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_01a01003-cadb-712d-bcb6-687e2c659d4f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_01a01003-cadb-70a8-becb-7817b98c76e5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_01a01003-cadb-712d-bcb6-687e2c659d4f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_01a01003-cadb-7c9d-bf8f-ba5002b24828" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_01a01003-cadb-70a8-becb-7817b98c76e5" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_01a01003-cadb-7c9d-bf8f-ba5002b24828" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_01a01003-cadb-715a-b5ff-d8062909af52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/INVESTMENTSAdditionalInformationDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#INVESTMENTSAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/INVESTMENTSAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a01003-cadb-7eda-bb49-7c8fbee9bf01" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a01003-cadb-7eda-bb49-7c8fbee9bf01" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_01a18600-a3ff-712c-b347-f09ddde93ea1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a01003-cadb-7eda-bb49-7c8fbee9bf01" xlink:to="loc_us-gaap_FinancialInstrumentAxis_01a18600-a3ff-712c-b347-f09ddde93ea1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_01a18600-a3ff-712c-b347-f09ddde93ea1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_01a18600-a3ff-712c-b347-f09ddde93ea1" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_01a18600-a3ff-712c-b347-f09ddde93ea1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_01a18600-a3ff-74c2-98a6-170ffdfec97c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_01a18600-a3ff-712c-b347-f09ddde93ea1" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_01a18600-a3ff-74c2-98a6-170ffdfec97c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_EquityLineOfCreditMember_01a18600-a3ff-751f-98fb-80e14fb54546" xlink:href="dfdv-20260930.xsd#dfdv_EquityLineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_01a18600-a3ff-74c2-98a6-170ffdfec97c" xlink:to="loc_dfdv_EquityLineOfCreditMember_01a18600-a3ff-751f-98fb-80e14fb54546" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_01a18601-59bf-7deb-9563-7edaba9c935e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a01003-cadb-7eda-bb49-7c8fbee9bf01" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_01a18601-59bf-7deb-9563-7edaba9c935e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a18601-59bf-7deb-9563-7edaba9c935e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_01a18601-59bf-7deb-9563-7edaba9c935e" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a18601-59bf-7deb-9563-7edaba9c935e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a18601-59bf-7196-a37c-1a1a3978bc99" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_01a18601-59bf-7deb-9563-7edaba9c935e" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a18601-59bf-7196-a37c-1a1a3978bc99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_JanoverProDispositionMember_01a18601-59bf-7f3e-b75e-98e6c003f53e" xlink:href="dfdv-20260930.xsd#dfdv_JanoverProDispositionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a18601-59bf-7196-a37c-1a1a3978bc99" xlink:to="loc_dfdv_JanoverProDispositionMember_01a18601-59bf-7f3e-b75e-98e6c003f53e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_01a18601-99fd-71a0-8a44-0c3d31e33311" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a01003-cadb-7eda-bb49-7c8fbee9bf01" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_01a18601-99fd-71a0-8a44-0c3d31e33311" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a18601-99fd-71a0-8a44-0c3d31e33311_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a18601-99fd-71a0-8a44-0c3d31e33311" xlink:to="loc_us-gaap_EquityComponentDomain_01a18601-99fd-71a0-8a44-0c3d31e33311_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_01a18601-99fd-7ea9-9d41-660aff7fb1a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_01a18601-99fd-71a0-8a44-0c3d31e33311" xlink:to="loc_us-gaap_EquityComponentDomain_01a18601-99fd-7ea9-9d41-660aff7fb1a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_PreFundedWarrantsMember_01a18601-99fd-7599-92c1-a5eda5d2b7a1" xlink:href="dfdv-20260930.xsd#dfdv_PreFundedWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a18601-99fd-7ea9-9d41-660aff7fb1a0" xlink:to="loc_dfdv_PreFundedWarrantsMember_01a18601-99fd-7599-92c1-a5eda5d2b7a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_CashWarrantsMember_01a18601-99fd-7a7b-a36c-45c76d58ebf9" xlink:href="dfdv-20260930.xsd#dfdv_CashWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_01a18601-99fd-7ea9-9d41-660aff7fb1a0" xlink:to="loc_dfdv_CashWarrantsMember_01a18601-99fd-7a7b-a36c-45c76d58ebf9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_01a18601-99fd-7c8e-a402-ab31e00e959e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a01003-cadb-7eda-bb49-7c8fbee9bf01" xlink:to="loc_us-gaap_TypeOfArrangementAxis_01a18601-99fd-7c8e-a402-ab31e00e959e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_01a18601-99fd-7c8e-a402-ab31e00e959e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_01a18601-99fd-7c8e-a402-ab31e00e959e" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_01a18601-99fd-7c8e-a402-ab31e00e959e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_01a18601-99fd-7345-8da0-dc919c1e2258" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_01a18601-99fd-7c8e-a402-ab31e00e959e" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_01a18601-99fd-7345-8da0-dc919c1e2258" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_SubscriptionAgreementMember_01a18601-99fd-7513-b03f-9599c47f1b73" xlink:href="dfdv-20260930.xsd#dfdv_SubscriptionAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_01a18601-99fd-7345-8da0-dc919c1e2258" xlink:to="loc_dfdv_SubscriptionAgreementMember_01a18601-99fd-7513-b03f-9599c47f1b73" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_SecuritiesPurchaseAgreementMember_01a18601-bf00-73ad-9d1b-42efb76e8a63" xlink:href="dfdv-20260930.xsd#dfdv_SecuritiesPurchaseAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_01a18601-99fd-7345-8da0-dc919c1e2258" xlink:to="loc_dfdv_SecuritiesPurchaseAgreementMember_01a18601-bf00-73ad-9d1b-42efb76e8a63" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a18601-99fd-7bbe-bcf1-44ef003d7e36" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a01003-cadb-7eda-bb49-7c8fbee9bf01" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a18601-99fd-7bbe-bcf1-44ef003d7e36" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_01a18601-99fd-7bbe-bcf1-44ef003d7e36_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a18601-99fd-7bbe-bcf1-44ef003d7e36" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_01a18601-99fd-7bbe-bcf1-44ef003d7e36_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_01a18601-99fd-7656-89cb-74ce4cd5b277" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_01a18601-99fd-7bbe-bcf1-44ef003d7e36" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_01a18601-99fd-7656-89cb-74ce4cd5b277" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_CykelAIMember_01a18601-99fd-71e3-9ae5-50cba9b7cd0e" xlink:href="dfdv-20260930.xsd#dfdv_CykelAIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_01a18601-99fd-7656-89cb-74ce4cd5b277" xlink:to="loc_dfdv_CykelAIMember_01a18601-99fd-71e3-9ae5-50cba9b7cd0e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_HBVSpecialOpportunitiesInvestmentHolding1LimitedMember_01a18601-99fd-7b01-b9d8-496e405f34cd" xlink:href="dfdv-20260930.xsd#dfdv_HBVSpecialOpportunitiesInvestmentHolding1LimitedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_01a18601-99fd-7656-89cb-74ce4cd5b277" xlink:to="loc_dfdv_HBVSpecialOpportunitiesInvestmentHolding1LimitedMember_01a18601-99fd-7b01-b9d8-496e405f34cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_01a18601-99fd-74cd-9c63-572abd91cfc5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a01003-cadb-7eda-bb49-7c8fbee9bf01" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_01a18601-99fd-74cd-9c63-572abd91cfc5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a18601-99fd-74cd-9c63-572abd91cfc5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_01a18601-99fd-74cd-9c63-572abd91cfc5" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a18601-99fd-74cd-9c63-572abd91cfc5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_01a18601-99fd-7b8f-beba-9d3505ddc87e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_01a18601-99fd-74cd-9c63-572abd91cfc5" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_01a18601-99fd-7b8f-beba-9d3505ddc87e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember_01a18601-99fd-7045-ab86-f9a06a2d5090" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_01a18601-99fd-7b8f-beba-9d3505ddc87e" xlink:to="loc_us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember_01a18601-99fd-7045-ab86-f9a06a2d5090" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a18601-99fd-7cc2-9ecc-bff5e8ea8fe2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a01003-cadb-7eda-bb49-7c8fbee9bf01" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a18601-99fd-7cc2-9ecc-bff5e8ea8fe2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a18601-99fd-7cc2-9ecc-bff5e8ea8fe2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a18601-99fd-7cc2-9ecc-bff5e8ea8fe2" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a18601-99fd-7cc2-9ecc-bff5e8ea8fe2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a18601-99fd-7a24-ae7e-01b90cc9b2ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_01a18601-99fd-7cc2-9ecc-bff5e8ea8fe2" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a18601-99fd-7a24-ae7e-01b90cc9b2ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_CykelAIMember_01a18601-99fd-782f-ba0d-fc540deb3fe1" xlink:href="dfdv-20260930.xsd#dfdv_CykelAIMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_01a18601-99fd-7a24-ae7e-01b90cc9b2ae" xlink:to="loc_dfdv_CykelAIMember_01a18601-99fd-782f-ba0d-fc540deb3fe1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_01a18601-99fd-7068-8c3e-20d271e9248d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a01003-cadb-7eda-bb49-7c8fbee9bf01" xlink:to="loc_dei_LegalEntityAxis_01a18601-99fd-7068-8c3e-20d271e9248d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a18601-99fd-7068-8c3e-20d271e9248d_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_01a18601-99fd-7068-8c3e-20d271e9248d" xlink:to="loc_dei_EntityDomain_01a18601-99fd-7068-8c3e-20d271e9248d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a18601-99fd-7e61-8d50-895bc26ea9ea" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_01a18601-99fd-7068-8c3e-20d271e9248d" xlink:to="loc_dei_EntityDomain_01a18601-99fd-7e61-8d50-895bc26ea9ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_HBVSpecialOpportunitiesInvestmentHolding1LimitedMember_01a18601-99fd-727d-9149-b6fbfdea78d8" xlink:href="dfdv-20260930.xsd#dfdv_HBVSpecialOpportunitiesInvestmentHolding1LimitedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a18601-99fd-7e61-8d50-895bc26ea9ea" xlink:to="loc_dfdv_HBVSpecialOpportunitiesInvestmentHolding1LimitedMember_01a18601-99fd-727d-9149-b6fbfdea78d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_HBVSpecialOpportunitiesLimitedPartnershipFundMember_01a18601-99fd-77ab-8119-b69f1f95263f" xlink:href="dfdv-20260930.xsd#dfdv_HBVSpecialOpportunitiesLimitedPartnershipFundMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a18601-99fd-7e61-8d50-895bc26ea9ea" xlink:to="loc_dfdv_HBVSpecialOpportunitiesLimitedPartnershipFundMember_01a18601-99fd-77ab-8119-b69f1f95263f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_01a18601-99fd-7e92-88bb-3518d964f703" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a01003-cadb-7eda-bb49-7c8fbee9bf01" xlink:to="loc_srt_OwnershipAxis_01a18601-99fd-7e92-88bb-3518d964f703" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_01a18601-99fd-7e92-88bb-3518d964f703_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_01a18601-99fd-7e92-88bb-3518d964f703" xlink:to="loc_srt_OwnershipDomain_01a18601-99fd-7e92-88bb-3518d964f703_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_01a18601-99fd-7a2f-bc15-7f6dac099bf5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_01a18601-99fd-7e92-88bb-3518d964f703" xlink:to="loc_srt_OwnershipDomain_01a18601-99fd-7a2f-bc15-7f6dac099bf5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_HBVSpecialOpportunitiesInvestmentHolding1LimitedMember_01a18601-99fd-7e67-93fb-34f1621bb91e" xlink:href="dfdv-20260930.xsd#dfdv_HBVSpecialOpportunitiesInvestmentHolding1LimitedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_01a18601-99fd-7a2f-bc15-7f6dac099bf5" xlink:to="loc_dfdv_HBVSpecialOpportunitiesInvestmentHolding1LimitedMember_01a18601-99fd-7e67-93fb-34f1621bb91e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CryptoAssetAxis_01a18601-bf00-7921-9e43-97681f7fae86" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CryptoAssetAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a01003-cadb-7eda-bb49-7c8fbee9bf01" xlink:to="loc_srt_CryptoAssetAxis_01a18601-bf00-7921-9e43-97681f7fae86" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CryptoAssetDomain_01a18601-bf00-7921-9e43-97681f7fae86_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CryptoAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CryptoAssetAxis_01a18601-bf00-7921-9e43-97681f7fae86" xlink:to="loc_srt_CryptoAssetDomain_01a18601-bf00-7921-9e43-97681f7fae86_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CryptoAssetDomain_01a18601-bf00-7a57-a99b-771d9c1a7c61" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_CryptoAssetDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CryptoAssetAxis_01a18601-bf00-7921-9e43-97681f7fae86" xlink:to="loc_srt_CryptoAssetDomain_01a18601-bf00-7a57-a99b-771d9c1a7c61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_SolanaMember_01a18601-bf00-7672-bf5f-4c2a74b8beec" xlink:href="dfdv-20260930.xsd#dfdv_SolanaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CryptoAssetDomain_01a18601-bf00-7a57-a99b-771d9c1a7c61" xlink:to="loc_dfdv_SolanaMember_01a18601-bf00-7672-bf5f-4c2a74b8beec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_01a18601-bf00-767a-93c0-71600c6c3a35" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_01a01003-cadb-7eda-bb49-7c8fbee9bf01" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_01a18601-bf00-767a-93c0-71600c6c3a35" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a18601-bf00-767a-93c0-71600c6c3a35_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a18601-bf00-767a-93c0-71600c6c3a35" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a18601-bf00-767a-93c0-71600c6c3a35_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a18601-bf00-7974-82d1-29b757402353" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a18601-bf00-767a-93c0-71600c6c3a35" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a18601-bf00-7974-82d1-29b757402353" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_ConvertibleNoteMember_01a18601-bf00-72f7-a7bf-61bc4202e3e2" xlink:href="dfdv-20260930.xsd#dfdv_ConvertibleNoteMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a18601-bf00-7974-82d1-29b757402353" xlink:to="loc_dfdv_ConvertibleNoteMember_01a18601-bf00-72f7-a7bf-61bc4202e3e2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_01a18600-a3ff-7e16-b4a0-537342b467c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_01a18600-a3ff-7e16-b4a0-537342b467c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_MarketableSecuritiesStockPurchaseObligation_01a18601-59bf-77f8-889f-2dbde7a492c9" xlink:href="dfdv-20260930.xsd#dfdv_MarketableSecuritiesStockPurchaseObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_dfdv_MarketableSecuritiesStockPurchaseObligation_01a18601-59bf-77f8-889f-2dbde7a492c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireMarketableSecurities_01a18601-59bf-74c8-b106-9b7485e035b7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireMarketableSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_PaymentsToAcquireMarketableSecurities_01a18601-59bf-74c8-b106-9b7485e035b7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleMaturityAndCollectionsOfInvestments_01a18601-59bf-7165-a4fa-39da53d41f28" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromSaleMaturityAndCollectionsOfInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_ProceedsFromSaleMaturityAndCollectionsOfInvestments_01a18601-59bf-7165-a4fa-39da53d41f28" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairments_01a18601-59bf-7557-9484-c0887fdacb64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MarketableSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_MarketableSecuritiesRealizedGainLossExcludingOtherThanTemporaryImpairments_01a18601-59bf-7557-9484-c0887fdacb64" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_01a18601-59bf-7ac7-8a1c-ff5525e1d62c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_01a18601-59bf-7ac7-8a1c-ff5525e1d62c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_NumberOfPrepaidWarrantsPurchased_01a18601-99fd-7ccc-aad1-98498e691317" xlink:href="dfdv-20260930.xsd#dfdv_NumberOfPrepaidWarrantsPurchased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_dfdv_NumberOfPrepaidWarrantsPurchased_01a18601-99fd-7ccc-aad1-98498e691317" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentAggregateCost_01a18601-99fd-7e44-8f89-38c7523412cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentAggregateCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_EquityMethodInvestmentAggregateCost_01a18601-99fd-7e44-8f89-38c7523412cc" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_01a18601-99fd-7731-b61f-39e6ffa21a31" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_01a18601-99fd-7731-b61f-39e6ffa21a31" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_PercentageOfPremiumExercisePriceOfWarrants_01a18601-99fd-7b92-a1c5-44b792cfa514" xlink:href="dfdv-20260930.xsd#dfdv_PercentageOfPremiumExercisePriceOfWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_dfdv_PercentageOfPremiumExercisePriceOfWarrants_01a18601-99fd-7b92-a1c5-44b792cfa514" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_EquityMethodInvestmentHoldingsSoldPercentage_01a18601-99fd-7934-934f-155f81859fca" xlink:href="dfdv-20260930.xsd#dfdv_EquityMethodInvestmentHoldingsSoldPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_dfdv_EquityMethodInvestmentHoldingsSoldPercentage_01a18601-99fd-7934-934f-155f81859fca" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentSoldCarryingAmount_01a18601-99fd-711f-a81d-f265d8f051b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentSoldCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_EquityMethodInvestmentSoldCarryingAmount_01a18601-99fd-711f-a81d-f265d8f051b0" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_EquityMethodInvestmentSharesPurchased_01a18601-99fd-7ea5-aeb1-046d6ed31227" xlink:href="dfdv-20260930.xsd#dfdv_EquityMethodInvestmentSharesPurchased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_dfdv_EquityMethodInvestmentSharesPurchased_01a18601-99fd-7ea5-aeb1-046d6ed31227" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_01a18601-99fd-7a65-90e4-7a1dd3466667" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_01a18601-99fd-7a65-90e4-7a1dd3466667" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireEquityMethodInvestments_01a18601-99fd-7d64-ad91-b8f8fae1c3f7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_PaymentsToAcquireEquityMethodInvestments_01a18601-99fd-7d64-ad91-b8f8fae1c3f7" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_01a18601-99fd-7e6e-b40c-09a943625aae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_01a18601-99fd-7e6e-b40c-09a943625aae" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_01a18601-99fd-7442-af5f-b98be1f2580a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_01a18601-99fd-7442-af5f-b98be1f2580a" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_01a18601-99fd-70c5-8268-4a9e0e42433c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_01a18601-99fd-70c5-8268-4a9e0e42433c" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_ConvertibleNotesReceivableInEquivalentCryptoCurrency_01a18601-bf00-7e1f-b99c-bcf37dc12e20" xlink:href="dfdv-20260930.xsd#dfdv_ConvertibleNotesReceivableInEquivalentCryptoCurrency"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_dfdv_ConvertibleNotesReceivableInEquivalentCryptoCurrency_01a18601-bf00-7e1f-b99c-bcf37dc12e20" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_01a18601-bf00-7738-aec5-78df63b4b364" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_01a18601-bf00-7738-aec5-78df63b4b364" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a18601-bf00-71a7-9864-b20997486db8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a18601-bf00-71a7-9864-b20997486db8" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDebtExtinguishmentCosts_01a18601-bf00-753d-8686-d39d569b7d54" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfDebtExtinguishmentCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_us-gaap_PaymentsOfDebtExtinguishmentCosts_01a18601-bf00-753d-8686-d39d569b7d54" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_EquityPaymentForDebtExtinguishmentOrDebtPrepaymentCost_01a18601-bf00-7dd5-8f73-b41441f9c420" xlink:href="dfdv-20260930.xsd#dfdv_EquityPaymentForDebtExtinguishmentOrDebtPrepaymentCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_dfdv_EquityPaymentForDebtExtinguishmentOrDebtPrepaymentCost_01a18601-bf00-7dd5-8f73-b41441f9c420" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DebtSecuritiesCurrentReceivedInPeriod_01a18601-bf00-7fd1-8513-5cba8b6d164a" xlink:href="dfdv-20260930.xsd#dfdv_DebtSecuritiesCurrentReceivedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_dfdv_DebtSecuritiesCurrentReceivedInPeriod_01a18601-bf00-7fd1-8513-5cba8b6d164a" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_SettlementOfNoteReceivableConsiderationReceived_01a18601-bf00-73ed-b711-00f08b00b4ae" xlink:href="dfdv-20260930.xsd#dfdv_SettlementOfNoteReceivableConsiderationReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_01a18600-a3ff-7acb-a749-3a2a75ce6750" xlink:to="loc_dfdv_SettlementOfNoteReceivableConsiderationReceived_01a18601-bf00-73ed-b711-00f08b00b4ae" xlink:type="arc" order="24"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/FAIRVALUEMEASUREMENTSScheduleofFinancialAssetsandLiabilitiesDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#FAIRVALUEMEASUREMENTSScheduleofFinancialAssetsandLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/FAIRVALUEMEASUREMENTSScheduleofFinancialAssetsandLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_FairValueMeasurementsScheduleofFinancialAssetsandLiabilitiesSubjecttoFairValueMeasurementsDetailsLineItems_01a01003-cadb-757d-bbcd-aa1ee2e5d027" xlink:href="dfdv-20260930.xsd#dfdv_FairValueMeasurementsScheduleofFinancialAssetsandLiabilitiesSubjecttoFairValueMeasurementsDetailsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_FairValueMeasurementsScheduleofFinancialAssetsandLiabilitiesSubjecttoFairValueMeasurementsDetailsTable_01a01003-cadb-7d6a-b50a-606382049d8f" xlink:href="dfdv-20260930.xsd#dfdv_FairValueMeasurementsScheduleofFinancialAssetsandLiabilitiesSubjecttoFairValueMeasurementsDetailsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dfdv_FairValueMeasurementsScheduleofFinancialAssetsandLiabilitiesSubjecttoFairValueMeasurementsDetailsLineItems_01a01003-cadb-757d-bbcd-aa1ee2e5d027" xlink:to="loc_dfdv_FairValueMeasurementsScheduleofFinancialAssetsandLiabilitiesSubjecttoFairValueMeasurementsDetailsTable_01a01003-cadb-7d6a-b50a-606382049d8f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_01a01003-cadb-74ea-8f5b-12d7278b9646" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dfdv_FairValueMeasurementsScheduleofFinancialAssetsandLiabilitiesSubjecttoFairValueMeasurementsDetailsTable_01a01003-cadb-7d6a-b50a-606382049d8f" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_01a01003-cadb-74ea-8f5b-12d7278b9646" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a01003-cadb-74ea-8f5b-12d7278b9646_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_01a01003-cadb-74ea-8f5b-12d7278b9646" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a01003-cadb-74ea-8f5b-12d7278b9646_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a01003-cadb-7e5f-8838-f013db2888bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_01a01003-cadb-74ea-8f5b-12d7278b9646" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a01003-cadb-7e5f-8838-f013db2888bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a01003-cadb-7887-8f02-459af65d48d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_01a01003-cadb-7e5f-8838-f013db2888bf" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a01003-cadb-7887-8f02-459af65d48d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_01a01003-cadb-7af1-b5f9-345bee3887c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a01003-cadb-7887-8f02-459af65d48d9" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_01a01003-cadb-7af1-b5f9-345bee3887c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_01a01003-cadb-7bd3-bb6b-13a9d675837d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_01a01003-cadb-7887-8f02-459af65d48d9" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_01a01003-cadb-7bd3-bb6b-13a9d675837d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a01003-cadb-7e91-bb68-e4161f8fb889" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dfdv_FairValueMeasurementsScheduleofFinancialAssetsandLiabilitiesSubjecttoFairValueMeasurementsDetailsTable_01a01003-cadb-7d6a-b50a-606382049d8f" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a01003-cadb-7e91-bb68-e4161f8fb889" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a01003-cadb-7e91-bb68-e4161f8fb889_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a01003-cadb-7e91-bb68-e4161f8fb889" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a01003-cadb-7e91-bb68-e4161f8fb889_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a01003-cadb-7e45-9c9b-92ab83a8d2cc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_01a01003-cadb-7e91-bb68-e4161f8fb889" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a01003-cadb-7e45-9c9b-92ab83a8d2cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_01a01003-cadb-7a3f-87cb-781d4f23c019" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a01003-cadb-7e45-9c9b-92ab83a8d2cc" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_01a01003-cadb-7a3f-87cb-781d4f23c019" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_01a01003-cadb-7313-b71f-687cdb8cb984" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a01003-cadb-7e45-9c9b-92ab83a8d2cc" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_01a01003-cadb-7313-b71f-687cdb8cb984" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_01a01003-cadb-73a8-8158-f896801bfe7b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_01a01003-cadb-7e45-9c9b-92ab83a8d2cc" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_01a01003-cadb-73a8-8158-f896801bfe7b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_01a01003-cadb-781a-a761-6738480a22d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dfdv_FairValueMeasurementsScheduleofFinancialAssetsandLiabilitiesSubjecttoFairValueMeasurementsDetailsLineItems_01a01003-cadb-757d-bbcd-aa1ee2e5d027" xlink:to="loc_us-gaap_AssetsAbstract_01a01003-cadb-781a-a761-6738480a22d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CryptoAssetFairValue_01a01003-cadb-7187-9cae-5e31846cf75e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CryptoAssetFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a01003-cadb-781a-a761-6738480a22d6" xlink:to="loc_us-gaap_CryptoAssetFairValue_01a01003-cadb-7187-9cae-5e31846cf75e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_CryptoAssetPledgedAsCollateralFairValue_01a01003-cadb-781b-a0a0-fbc397442b89" xlink:href="dfdv-20260930.xsd#dfdv_CryptoAssetPledgedAsCollateralFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a01003-cadb-781a-a761-6738480a22d6" xlink:to="loc_dfdv_CryptoAssetPledgedAsCollateralFairValue_01a01003-cadb-781b-a0a0-fbc397442b89" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetsStableCoinsFairValueDisclosure_01a01003-cadb-7930-aba8-2e5a62c457af" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetsStableCoinsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a01003-cadb-781a-a761-6738480a22d6" xlink:to="loc_dfdv_DigitalAssetsStableCoinsFairValueDisclosure_01a01003-cadb-7930-aba8-2e5a62c457af" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DebtSecuritiesFairValueDisclosure_01a01003-cadb-7949-a236-fa9a33969122" xlink:href="dfdv-20260930.xsd#dfdv_DebtSecuritiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a01003-cadb-781a-a761-6738480a22d6" xlink:to="loc_dfdv_DebtSecuritiesFairValueDisclosure_01a01003-cadb-7949-a236-fa9a33969122" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_MarketableSecuritiesFairValueDisclosure_01a01003-cadb-7141-a5fb-810f26ef1e53" xlink:href="dfdv-20260930.xsd#dfdv_MarketableSecuritiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a01003-cadb-781a-a761-6738480a22d6" xlink:to="loc_dfdv_MarketableSecuritiesFairValueDisclosure_01a01003-cadb-7141-a5fb-810f26ef1e53" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_01a01003-cadb-7b35-99d4-f77656a0534b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_01a01003-cadb-781a-a761-6738480a22d6" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_01a01003-cadb-7b35-99d4-f77656a0534b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract_01a01003-cadb-7bcf-87f6-2eeb120be812" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dfdv_FairValueMeasurementsScheduleofFinancialAssetsandLiabilitiesSubjecttoFairValueMeasurementsDetailsLineItems_01a01003-cadb-757d-bbcd-aa1ee2e5d027" xlink:to="loc_us-gaap_LiabilitiesAbstract_01a01003-cadb-7bcf-87f6-2eeb120be812" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_CryptoAssetFinancingArrangementFairValueDisclosure_01a01003-cadb-72a6-8870-db99ce168d72" xlink:href="dfdv-20260930.xsd#dfdv_CryptoAssetFinancingArrangementFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_01a01003-cadb-7bcf-87f6-2eeb120be812" xlink:to="loc_dfdv_CryptoAssetFinancingArrangementFairValueDisclosure_01a01003-cadb-72a6-8870-db99ce168d72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_01a01003-cadb-7e56-ae9a-8e21e3a4361a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_01a01003-cadb-7bcf-87f6-2eeb120be812" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_01a01003-cadb-7e56-ae9a-8e21e3a4361a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_01a01003-cadb-7aa8-bb01-2b9a86b8bb12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract_01a01003-cadb-7bcf-87f6-2eeb120be812" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_01a01003-cadb-7aa8-bb01-2b9a86b8bb12" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/FAIRVALUEMEASUREMENTSAdditionalInformationDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#FAIRVALUEMEASUREMENTSAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/FAIRVALUEMEASUREMENTSAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_01a01003-cadb-7503-93d0-2b934653e346" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_01a01003-cadb-7249-9a64-27c568650f26" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_01a01003-cadb-7503-93d0-2b934653e346" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_01a01003-cadb-7249-9a64-27c568650f26" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_01a01003-cadb-74a5-a6f4-d49b5d504a3b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_01a01003-cadb-7249-9a64-27c568650f26" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_01a01003-cadb-74a5-a6f4-d49b5d504a3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a01003-cadb-74a5-a6f4-d49b5d504a3b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a01003-cadb-74a5-a6f4-d49b5d504a3b" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a01003-cadb-74a5-a6f4-d49b5d504a3b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a01003-cadb-76de-a79d-507b9f5e6a1a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a01003-cadb-74a5-a6f4-d49b5d504a3b" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a01003-cadb-76de-a79d-507b9f5e6a1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_WarrantDividendMember_01a01003-cadb-7c42-a885-920575153a9f" xlink:href="dfdv-20260930.xsd#dfdv_WarrantDividendMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a01003-cadb-76de-a79d-507b9f5e6a1a" xlink:to="loc_dfdv_WarrantDividendMember_01a01003-cadb-7c42-a885-920575153a9f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_WarrantDividendSeries1Member_01a01003-cadb-7034-a9ca-948f148dd447" xlink:href="dfdv-20260930.xsd#dfdv_WarrantDividendSeries1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dfdv_WarrantDividendMember_01a01003-cadb-7c42-a885-920575153a9f" xlink:to="loc_dfdv_WarrantDividendSeries1Member_01a01003-cadb-7034-a9ca-948f148dd447" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_WarrantDividendSeries2Member_01a01003-cadb-737d-8dc7-e48bdcde3c4d" xlink:href="dfdv-20260930.xsd#dfdv_WarrantDividendSeries2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dfdv_WarrantDividendMember_01a01003-cadb-7c42-a885-920575153a9f" xlink:to="loc_dfdv_WarrantDividendSeries2Member_01a01003-cadb-737d-8dc7-e48bdcde3c4d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetImpairmentCharges_01a01003-cadb-79b6-8aac-eda8a2d7b85d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_01a01003-cadb-7503-93d0-2b934653e346" xlink:to="loc_us-gaap_AssetImpairmentCharges_01a01003-cadb-79b6-8aac-eda8a2d7b85d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_WarrantDividendFairValue_01a01003-cadb-7cc1-a943-2eb0fbc73e0a" xlink:href="dfdv-20260930.xsd#dfdv_WarrantDividendFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_01a01003-cadb-7503-93d0-2b934653e346" xlink:to="loc_dfdv_WarrantDividendFairValue_01a01003-cadb-7cc1-a943-2eb0fbc73e0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_01a01003-cadb-7471-9883-65a46329876a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_01a01003-cadb-7503-93d0-2b934653e346" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_01a01003-cadb-7471-9883-65a46329876a" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/FAIRVALUEMEASUREMENTSScheduleofFairValueMeasurementInputsandValuationTechniquesDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#FAIRVALUEMEASUREMENTSScheduleofFairValueMeasurementInputsandValuationTechniquesDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/FAIRVALUEMEASUREMENTSScheduleofFairValueMeasurementInputsandValuationTechniquesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_01a01003-cadb-7cd3-9f83-759f10612b5c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_01a01003-cadb-7283-b6d1-8d7289029b42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_01a01003-cadb-7cd3-9f83-759f10612b5c" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_01a01003-cadb-7283-b6d1-8d7289029b42" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_01a01003-cadb-7454-a694-20cafc56720b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_01a01003-cadb-7283-b6d1-8d7289029b42" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_01a01003-cadb-7454-a694-20cafc56720b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a01003-cadb-7454-a694-20cafc56720b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a01003-cadb-7454-a694-20cafc56720b" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a01003-cadb-7454-a694-20cafc56720b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a01003-cadb-7d57-9296-d08a5806299f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a01003-cadb-7454-a694-20cafc56720b" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a01003-cadb-7d57-9296-d08a5806299f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_WarrantDividendMember_01a01003-cadb-746d-865c-0d24127ab260" xlink:href="dfdv-20260930.xsd#dfdv_WarrantDividendMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a01003-cadb-7d57-9296-d08a5806299f" xlink:to="loc_dfdv_WarrantDividendMember_01a01003-cadb-746d-865c-0d24127ab260" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_01a01003-cadb-7d53-84e6-d01a77754173" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_01a01003-cadb-7283-b6d1-8d7289029b42" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_01a01003-cadb-7d53-84e6-d01a77754173" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_01a01003-cadb-7d53-84e6-d01a77754173_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_01a01003-cadb-7d53-84e6-d01a77754173" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_01a01003-cadb-7d53-84e6-d01a77754173_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_01a01003-cadb-79ba-8d40-048c21696fa7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_01a01003-cadb-7d53-84e6-d01a77754173" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_01a01003-cadb-79ba-8d40-048c21696fa7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputSharePriceMember_01a01003-cadb-7bb2-bf4f-d92707a700e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputSharePriceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_01a01003-cadb-79ba-8d40-048c21696fa7" xlink:to="loc_us-gaap_MeasurementInputSharePriceMember_01a01003-cadb-7bb2-bf4f-d92707a700e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_MeasurementInputStrikePriceSeries1Member_01a01003-cadb-7399-ad95-04636f4aca4e" xlink:href="dfdv-20260930.xsd#dfdv_MeasurementInputStrikePriceSeries1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_01a01003-cadb-79ba-8d40-048c21696fa7" xlink:to="loc_dfdv_MeasurementInputStrikePriceSeries1Member_01a01003-cadb-7399-ad95-04636f4aca4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_MeasurementInputStrikePriceSeries2Member_01a01003-cadb-7317-bee0-ce5543779f50" xlink:href="dfdv-20260930.xsd#dfdv_MeasurementInputStrikePriceSeries2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_01a01003-cadb-79ba-8d40-048c21696fa7" xlink:to="loc_dfdv_MeasurementInputStrikePriceSeries2Member_01a01003-cadb-7317-bee0-ce5543779f50" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_MeasurementInputDividendMember_01a01003-cadb-76ff-9609-fb155a390eb3" xlink:href="dfdv-20260930.xsd#dfdv_MeasurementInputDividendMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_01a01003-cadb-79ba-8d40-048c21696fa7" xlink:to="loc_dfdv_MeasurementInputDividendMember_01a01003-cadb-76ff-9609-fb155a390eb3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_01a01003-cadb-744f-b02b-5ccff15ef39b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_01a01003-cadb-79ba-8d40-048c21696fa7" xlink:to="loc_us-gaap_MeasurementInputRiskFreeInterestRateMember_01a01003-cadb-744f-b02b-5ccff15ef39b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputExpectedTermMember_01a01003-cadb-7c1b-bcea-50ae7b9d5cf0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputExpectedTermMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_01a01003-cadb-79ba-8d40-048c21696fa7" xlink:to="loc_us-gaap_MeasurementInputExpectedTermMember_01a01003-cadb-7c1b-bcea-50ae7b9d5cf0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputPriceVolatilityMember_01a01003-cadb-7f8a-96ed-3ca7d177d30c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MeasurementInputPriceVolatilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_01a01003-cadb-79ba-8d40-048c21696fa7" xlink:to="loc_us-gaap_MeasurementInputPriceVolatilityMember_01a01003-cadb-7f8a-96ed-3ca7d177d30c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_01a01003-cadb-7735-8432-e6953b481fed" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstandingMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_01a01003-cadb-7cd3-9f83-759f10612b5c" xlink:to="loc_us-gaap_WarrantsAndRightsOutstandingMeasurementInput_01a01003-cadb-7735-8432-e6953b481fed" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/COMMITMENTSANDCONTINGENCIESDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#COMMITMENTSANDCONTINGENCIESDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/COMMITMENTSANDCONTINGENCIESDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsLineItems_01a01003-cadb-7ee3-9bcc-eb0eb4136f7d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCommitmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_CommitmentsandContingenciesDetailsTable_01a01003-cadb-7c33-a772-6ac0c78ae423" xlink:href="dfdv-20260930.xsd#dfdv_CommitmentsandContingenciesDetailsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_01a01003-cadb-7ee3-9bcc-eb0eb4136f7d" xlink:to="loc_dfdv_CommitmentsandContingenciesDetailsTable_01a01003-cadb-7c33-a772-6ac0c78ae423" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_01a01003-cadb-75da-b920-824e3fa26a52" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dfdv_CommitmentsandContingenciesDetailsTable_01a01003-cadb-7c33-a772-6ac0c78ae423" xlink:to="loc_us-gaap_CreditFacilityAxis_01a01003-cadb-75da-b920-824e3fa26a52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a01003-cadb-75da-b920-824e3fa26a52_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_01a01003-cadb-75da-b920-824e3fa26a52" xlink:to="loc_us-gaap_CreditFacilityDomain_01a01003-cadb-75da-b920-824e3fa26a52_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_01a01003-cadb-740a-91d9-7ebe20ebdafb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_01a01003-cadb-75da-b920-824e3fa26a52" xlink:to="loc_us-gaap_CreditFacilityDomain_01a01003-cadb-740a-91d9-7ebe20ebdafb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_01a01003-cadb-721f-9204-4f2a03696a70" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_01a01003-cadb-740a-91d9-7ebe20ebdafb" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_01a01003-cadb-721f-9204-4f2a03696a70" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_01a01003-cadb-78a3-a12f-55cc2a824798" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dfdv_CommitmentsandContingenciesDetailsTable_01a01003-cadb-7c33-a772-6ac0c78ae423" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_01a01003-cadb-78a3-a12f-55cc2a824798" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a01003-cadb-78a3-a12f-55cc2a824798_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a01003-cadb-78a3-a12f-55cc2a824798" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a01003-cadb-78a3-a12f-55cc2a824798_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_01a01003-cadb-70bd-bf57-53702a5de8e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_01a01003-cadb-78a3-a12f-55cc2a824798" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_01a01003-cadb-70bd-bf57-53702a5de8e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_PromissoryNoteAgreementMember_01a01003-cadb-7f89-bdea-d24577dffacf" xlink:href="dfdv-20260930.xsd#dfdv_PromissoryNoteAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_01a01003-cadb-70bd-bf57-53702a5de8e5" xlink:to="loc_dfdv_PromissoryNoteAgreementMember_01a01003-cadb-7f89-bdea-d24577dffacf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_01a01003-cadb-7e3f-8e2d-6f2942084129" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dfdv_CommitmentsandContingenciesDetailsTable_01a01003-cadb-7c33-a772-6ac0c78ae423" xlink:to="loc_dei_LegalEntityAxis_01a01003-cadb-7e3f-8e2d-6f2942084129" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a01003-cadb-7e3f-8e2d-6f2942084129_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_01a01003-cadb-7e3f-8e2d-6f2942084129" xlink:to="loc_dei_EntityDomain_01a01003-cadb-7e3f-8e2d-6f2942084129_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_01a01003-cadb-75c4-bd97-14c6825a5801" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_01a01003-cadb-7e3f-8e2d-6f2942084129" xlink:to="loc_dei_EntityDomain_01a01003-cadb-75c4-bd97-14c6825a5801" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_UnnamedEquityMethodInvestmentMember_01a01003-cadb-7f09-a3c1-ce3e4dea07eb" xlink:href="dfdv-20260930.xsd#dfdv_UnnamedEquityMethodInvestmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_01a01003-cadb-75c4-bd97-14c6825a5801" xlink:to="loc_dfdv_UnnamedEquityMethodInvestmentMember_01a01003-cadb-7f09-a3c1-ce3e4dea07eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_01a01003-cadb-7a92-872a-807cadb1f9fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_01a01003-cadb-7ee3-9bcc-eb0eb4136f7d" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_01a01003-cadb-7a92-872a-807cadb1f9fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTerm_01a01003-cadb-7a96-a908-c42fda5ed158" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_01a01003-cadb-7ee3-9bcc-eb0eb4136f7d" xlink:to="loc_us-gaap_DebtInstrumentTerm_01a01003-cadb-7a96-a908-c42fda5ed158" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityInterestRateDuringPeriod_01a01003-cadb-7653-bc53-83e658d760d4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityInterestRateDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_01a01003-cadb-7ee3-9bcc-eb0eb4136f7d" xlink:to="loc_us-gaap_LineOfCreditFacilityInterestRateDuringPeriod_01a01003-cadb-7653-bc53-83e658d760d4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_LineOfCreditFacilityPeriodicPaymentInterestPeriod_01a01003-cadb-7e35-8077-89a816f637d6" xlink:href="dfdv-20260930.xsd#dfdv_LineOfCreditFacilityPeriodicPaymentInterestPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_01a01003-cadb-7ee3-9bcc-eb0eb4136f7d" xlink:to="loc_dfdv_LineOfCreditFacilityPeriodicPaymentInterestPeriod_01a01003-cadb-7e35-8077-89a816f637d6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_01a01003-cadb-7a97-92f9-f100a7e09c26" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_01a01003-cadb-7ee3-9bcc-eb0eb4136f7d" xlink:to="loc_us-gaap_LineOfCredit_01a01003-cadb-7a97-92f9-f100a7e09c26" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ExtinguishmentOfDebtAmount_01a01003-cadb-7665-a78b-15b22010fef3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ExtinguishmentOfDebtAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_01a01003-cadb-7ee3-9bcc-eb0eb4136f7d" xlink:to="loc_us-gaap_ExtinguishmentOfDebtAmount_01a01003-cadb-7665-a78b-15b22010fef3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_01a01003-cadb-7662-8590-b51659db096a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_01a01003-cadb-7ee3-9bcc-eb0eb4136f7d" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_01a01003-cadb-7662-8590-b51659db096a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_01a01003-cadb-70dd-9e5e-62d8db2cd3f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_01a01003-cadb-7ee3-9bcc-eb0eb4136f7d" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_01a01003-cadb-70dd-9e5e-62d8db2cd3f4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a01003-cadb-753b-aac3-ec6f27bfe5af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_01a01003-cadb-7ee3-9bcc-eb0eb4136f7d" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_01a01003-cadb-753b-aac3-ec6f27bfe5af" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterest_01a01003-cadb-7d05-989b-3da11affe163" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_01a01003-cadb-7ee3-9bcc-eb0eb4136f7d" xlink:to="loc_us-gaap_InvestmentIncomeInterest_01a01003-cadb-7d05-989b-3da11affe163" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/OFFBALANCESHEETTRANSACTIONSDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#OFFBALANCESHEETTRANSACTIONSDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/OFFBALANCESHEETTRANSACTIONSDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_01a01003-cadb-7d92-93a1-16cf1b795a35" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a01003-cadb-72ca-ba86-46586ec620ad" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01003-cadb-7d92-93a1-16cf1b795a35" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a01003-cadb-72ca-ba86-46586ec620ad" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_01a01003-cadb-77eb-975c-51867e7e310a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_01a01003-cadb-72ca-ba86-46586ec620ad" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_01a01003-cadb-77eb-975c-51867e7e310a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01003-cadb-77eb-975c-51867e7e310a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_01a01003-cadb-77eb-975c-51867e7e310a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01003-cadb-77eb-975c-51867e7e310a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01003-cadb-70a7-a8ba-2a3269140952" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_01a01003-cadb-77eb-975c-51867e7e310a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01003-cadb-70a7-a8ba-2a3269140952" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_SOLMember_01a01003-cadb-797d-b6cf-5f792b0ed13a" xlink:href="dfdv-20260930.xsd#dfdv_SOLMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a01003-cadb-70a7-a8ba-2a3269140952" xlink:to="loc_dfdv_SOLMember_01a01003-cadb-797d-b6cf-5f792b0ed13a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_NumberOfTokensDelegatedToCustomers_01a01003-cadb-79f7-88a5-b9d71d4dca7c" xlink:href="dfdv-20260930.xsd#dfdv_NumberOfTokensDelegatedToCustomers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01003-cadb-7d92-93a1-16cf1b795a35" xlink:to="loc_dfdv_NumberOfTokensDelegatedToCustomers_01a01003-cadb-79f7-88a5-b9d71d4dca7c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_TokensDelegatedAmountToValidators_01a01003-cadb-755e-822e-de0604ae8c80" xlink:href="dfdv-20260930.xsd#dfdv_TokensDelegatedAmountToValidators"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_01a01003-cadb-7d92-93a1-16cf1b795a35" xlink:to="loc_dfdv_TokensDelegatedAmountToValidators_01a01003-cadb-755e-822e-de0604ae8c80" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/RELATEDPARTYTRANSACTIONSDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#RELATEDPARTYTRANSACTIONSDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/RELATEDPARTYTRANSACTIONSDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_01a01003-cadb-79f6-9779-5e8ef8fb2179" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a01003-cadb-7b85-a9e9-5e0b86dad4fb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a01003-cadb-79f6-9779-5e8ef8fb2179" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a01003-cadb-7b85-a9e9-5e0b86dad4fb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a01003-cadb-73c7-83bb-d42936437035" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_01a01003-cadb-7b85-a9e9-5e0b86dad4fb" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a01003-cadb-73c7-83bb-d42936437035" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a01003-cadb-73c7-83bb-d42936437035_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a01003-cadb-73c7-83bb-d42936437035" xlink:to="loc_us-gaap_RelatedPartyDomain_01a01003-cadb-73c7-83bb-d42936437035_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_01a01003-cadb-7eee-b114-4661fabb1af6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_01a01003-cadb-73c7-83bb-d42936437035" xlink:to="loc_us-gaap_RelatedPartyDomain_01a01003-cadb-7eee-b114-4661fabb1af6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_Mr.JanoverMember_01a01003-cadb-7570-bd8b-ea28a524540c" xlink:href="dfdv-20260930.xsd#dfdv_Mr.JanoverMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_01a01003-cadb-7eee-b114-4661fabb1af6" xlink:to="loc_dfdv_Mr.JanoverMember_01a01003-cadb-7570-bd8b-ea28a524540c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_01a01003-cadb-73b5-8aa2-5be641a3ca78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAmountsOfTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a01003-cadb-79f6-9779-5e8ef8fb2179" xlink:to="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_01a01003-cadb-73b5-8aa2-5be641a3ca78" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_01a01003-cadb-7543-95a1-a0443505e29f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_01a01003-cadb-79f6-9779-5e8ef8fb2179" xlink:to="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_01a01003-cadb-7543-95a1-a0443505e29f" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://defidevcorp.com/role/SUBSEQUENTEVENTSDetails" xlink:type="simple" xlink:href="dfdv-20260930.xsd#SUBSEQUENTEVENTSDetails"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/SUBSEQUENTEVENTSDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_01a01003-cadb-7242-8695-674829ddf638" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_01a01003-cadb-7ca9-993e-5f3006809bf4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_01a01003-cadb-7242-8695-674829ddf638" xlink:to="loc_us-gaap_SubsequentEventTable_01a01003-cadb-7ca9-993e-5f3006809bf4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_01a01003-cadb-7a14-af07-7856cb2bbe4d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_01a01003-cadb-7ca9-993e-5f3006809bf4" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_01a01003-cadb-7a14-af07-7856cb2bbe4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_01a01003-cadb-7a14-af07-7856cb2bbe4d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_01a01003-cadb-7a14-af07-7856cb2bbe4d" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_01a01003-cadb-7a14-af07-7856cb2bbe4d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_01a01003-cadb-7d13-8420-5f6989e18d72" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_01a01003-cadb-7a14-af07-7856cb2bbe4d" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_01a01003-cadb-7d13-8420-5f6989e18d72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_01a01003-cadb-7fb9-8df2-e8986b95390d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_01a01003-cadb-7d13-8420-5f6989e18d72" xlink:to="loc_us-gaap_SubsequentEventMember_01a01003-cadb-7fb9-8df2-e8986b95390d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_01a01003-cadb-7a93-97ff-e19e6d461881" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_01a01003-cadb-7ca9-993e-5f3006809bf4" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_01a01003-cadb-7a93-97ff-e19e6d461881" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a01003-cadb-7a93-97ff-e19e6d461881_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_01a01003-cadb-7a93-97ff-e19e6d461881" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a01003-cadb-7a93-97ff-e19e6d461881_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a01003-cadb-7ea4-8365-8ec42b5e4337" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_01a01003-cadb-7a93-97ff-e19e6d461881" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a01003-cadb-7ea4-8365-8ec42b5e4337" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_AtTheMarketOfferingMember_01a01003-cadb-7822-9790-53e494b0788a" xlink:href="dfdv-20260930.xsd#dfdv_AtTheMarketOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_01a01003-cadb-7ea4-8365-8ec42b5e4337" xlink:to="loc_dfdv_AtTheMarketOfferingMember_01a01003-cadb-7822-9790-53e494b0788a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_01a1af82-230c-7715-8e83-35a80b0ef371" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_01a01003-cadb-7ca9-993e-5f3006809bf4" xlink:to="loc_us-gaap_StatementClassOfStockAxis_01a1af82-230c-7715-8e83-35a80b0ef371" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a1af82-230c-7715-8e83-35a80b0ef371_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a1af82-230c-7715-8e83-35a80b0ef371" xlink:to="loc_us-gaap_ClassOfStockDomain_01a1af82-230c-7715-8e83-35a80b0ef371_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a1af82-230c-7678-82aa-915bf2cb5861" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a1af82-230c-7715-8e83-35a80b0ef371" xlink:to="loc_us-gaap_ClassOfStockDomain_01a1af82-230c-7678-82aa-915bf2cb5861" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemablePreferredStockMember_01a1c125-41a4-77b3-b03d-eab3b293aaab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RedeemablePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a1af82-230c-7678-82aa-915bf2cb5861" xlink:to="loc_us-gaap_RedeemablePreferredStockMember_01a1c125-41a4-77b3-b03d-eab3b293aaab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_01a1af83-d82e-71fe-9a4a-907c84d03487" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_01a01003-cadb-7ca9-993e-5f3006809bf4" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_01a1af83-d82e-71fe-9a4a-907c84d03487" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a1af83-d82e-71fe-9a4a-907c84d03487_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a1af83-d82e-71fe-9a4a-907c84d03487" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a1af83-d82e-71fe-9a4a-907c84d03487_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_01a1af83-d82e-74f2-b0be-af483d723106" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_01a1af83-d82e-71fe-9a4a-907c84d03487" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_01a1af83-d82e-74f2-b0be-af483d723106" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_PreFundedWarrantsMember_01a1860c-c800-7cd5-9d66-193db4ad4ae8" xlink:href="dfdv-20260930.xsd#dfdv_PreFundedWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_01a1af83-d82e-74f2-b0be-af483d723106" xlink:to="loc_dfdv_PreFundedWarrantsMember_01a1860c-c800-7cd5-9d66-193db4ad4ae8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_01a01003-cadb-7354-95b6-0936eba5550d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_01a01003-cadb-7242-8695-674829ddf638" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_01a01003-cadb-7354-95b6-0936eba5550d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_01a01003-cadb-7cd7-a0bd-7b548b76e25f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_01a01003-cadb-7242-8695-674829ddf638" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_01a01003-cadb-7cd7-a0bd-7b548b76e25f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_01a1af83-4ae3-7a8c-9568-edab68f56fc6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_01a01003-cadb-7242-8695-674829ddf638" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_01a1af83-4ae3-7a8c-9568-edab68f56fc6" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/srt/role/srt-eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-roles-2026.xsd#eedm1"/>
  <link:definitionLink xlink:role="http://fasb.org/srt/role/srt-eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetsPledgedAsCollateral_01a01003-c811-785f-bcb4-e8c638afaec0" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetsPledgedAsCollateral"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="loc_dfdv_DigitalAssetsPledgedAsCollateral_01a01003-c811-785f-bcb4-e8c638afaec0" xlink:type="arc" order="101"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_dfdv_DigitalAssetFinancingArrangements_01a01003-c811-763a-9ffb-336eb522b9b4" xlink:href="dfdv-20260930.xsd#dfdv_DigitalAssetFinancingArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAbstract" xlink:to="loc_dfdv_DigitalAssetFinancingArrangements_01a01003-c811-763a-9ffb-336eb522b9b4" xlink:type="arc" order="31"/>
  </link:definitionLink>
</link:linkbase>
