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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:01a05976-130f-7e07-8970-84ad79dfae2d,g:cb600520-11de-4b83-bce0-be9f667335a3-->
<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/Cover" xlink:type="simple" xlink:href="dfdv-20260831.xsd#Cover"/>
  <link:definitionLink xlink:role="http://defidevcorp.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_01a05976-130f-7278-9c11-27ffb663df6a" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_DocumentInformationTable_01a05976-130f-7278-9c11-27ffb663df6a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_01a05976-130f-72f2-a150-f672619fe11b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_01a05976-130f-7278-9c11-27ffb663df6a" xlink:to="loc_us-gaap_StatementClassOfStockAxis_01a05976-130f-72f2-a150-f672619fe11b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a05976-130f-72f2-a150-f672619fe11b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a05976-130f-72f2-a150-f672619fe11b" xlink:to="loc_us-gaap_ClassOfStockDomain_01a05976-130f-72f2-a150-f672619fe11b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a05976-130f-71a3-b66d-c8f75da711af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_01a05976-130f-72f2-a150-f672619fe11b" xlink:to="loc_us-gaap_ClassOfStockDomain_01a05976-130f-71a3-b66d-c8f75da711af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_DFDV_CommonStockParValue0.00001PerShareMember_01a05976-130f-79b4-b13a-fc41e5393349" xlink:href="dfdv-20260831.xsd#DFDV_CommonStockParValue0.00001PerShareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a05976-130f-71a3-b66d-c8f75da711af" xlink:to="loc_DFDV_CommonStockParValue0.00001PerShareMember_01a05976-130f-79b4-b13a-fc41e5393349" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_DFDV_WarrantsEachWarrantExercisableForOneShareOfCommonStockMember_01a05976-130f-765a-a73e-1063f8d55c19" xlink:href="dfdv-20260831.xsd#DFDV_WarrantsEachWarrantExercisableForOneShareOfCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a05976-130f-71a3-b66d-c8f75da711af" xlink:to="loc_DFDV_WarrantsEachWarrantExercisableForOneShareOfCommonStockMember_01a05976-130f-765a-a73e-1063f8d55c19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_01a05976-130f-729a-b8f8-307c20975c44" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_DocumentType_01a05976-130f-729a-b8f8-307c20975c44" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_01a05976-130f-7db6-b08b-fd1ea161aa28" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_DocumentPeriodEndDate_01a05976-130f-7db6-b08b-fd1ea161aa28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_01a05976-130f-7589-adc9-b67fbdd264e8" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_EntityRegistrantName_01a05976-130f-7589-adc9-b67fbdd264e8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_01a05976-130f-7665-baad-b492796f4aa2" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_EntityIncorporationStateCountryCode_01a05976-130f-7665-baad-b492796f4aa2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_01a05976-130f-75d5-9a3c-802825b83240" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_EntityFileNumber_01a05976-130f-75d5-9a3c-802825b83240" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_01a05976-130f-731c-9aca-12775276cd5e" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_EntityTaxIdentificationNumber_01a05976-130f-731c-9aca-12775276cd5e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_01a05976-130f-7e87-a7a4-f6143675b722" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_EntityAddressAddressLine1_01a05976-130f-7e87-a7a4-f6143675b722" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_01a05976-130f-7e6e-8ca5-739c808e5e70" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_EntityAddressAddressLine2_01a05976-130f-7e6e-8ca5-739c808e5e70" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_01a05976-130f-73b7-8a37-41e8b9a54557" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_EntityAddressCityOrTown_01a05976-130f-73b7-8a37-41e8b9a54557" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_01a05976-130f-7896-a517-f875ed902642" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_EntityAddressStateOrProvince_01a05976-130f-7896-a517-f875ed902642" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_01a05976-130f-7c8c-935f-b4eed90fa572" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_EntityAddressPostalZipCode_01a05976-130f-7c8c-935f-b4eed90fa572" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_01a05976-130f-70aa-8a98-59a2edb80edb" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_CityAreaCode_01a05976-130f-70aa-8a98-59a2edb80edb" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_01a05976-130f-7f82-bde2-35816358a3ef" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_LocalPhoneNumber_01a05976-130f-7f82-bde2-35816358a3ef" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_01a05976-130f-7bdc-b0e6-d63c17b2badf" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_WrittenCommunications_01a05976-130f-7bdc-b0e6-d63c17b2badf" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_01a05976-130f-7117-954f-8f09c0f3129b" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_SolicitingMaterial_01a05976-130f-7117-954f-8f09c0f3129b" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_01a05976-130f-74d3-ac77-aa6d28ccc5e9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_PreCommencementTenderOffer_01a05976-130f-74d3-ac77-aa6d28ccc5e9" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_01a05976-130f-78d8-a0d8-c0a34c8052e7" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_01a05976-130f-78d8-a0d8-c0a34c8052e7" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_01a05976-130f-732e-999a-d60bcacc8b8f" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_Security12bTitle_01a05976-130f-732e-999a-d60bcacc8b8f" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_01a05976-130f-73b3-b7b8-11954b633ee8" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_TradingSymbol_01a05976-130f-73b3-b7b8-11954b633ee8" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_01a05976-130f-789d-a2b7-fe72400ee466" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_SecurityExchangeName_01a05976-130f-789d-a2b7-fe72400ee466" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_01a05976-130f-7ae6-b248-3e349796f456" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_EntityEmergingGrowthCompany_01a05976-130f-7ae6-b248-3e349796f456" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityExTransitionPeriod_01a05976-130f-7256-9699-a5a1ae5d94a0" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityExTransitionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_EntityExTransitionPeriod_01a05976-130f-7256-9699-a5a1ae5d94a0" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_01a05976-130f-7be9-b342-4f013aca9ffc" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_AmendmentFlag_01a05976-130f-7be9-b342-4f013aca9ffc" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_01a05976-130f-71e8-a07f-0ae00f8e31be" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05976-130f-7e15-8595-5e10a9f96d9c" xlink:to="loc_dei_EntityCentralIndexKey_01a05976-130f-71e8-a07f-0ae00f8e31be" xlink:type="arc" order="23"/>
  </link:definitionLink>
</link:linkbase>
