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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019e183d-345f-767a-bcd8-886b02da62e4,g:3fb23b35-4c06-4d60-843b-4dc80bc1f394-->
<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://janusreit.com/role/COVERPAGE" xlink:type="simple" xlink:href="jan-20260804.xsd#COVERPAGE"/>
  <link:definitionLink xlink:role="http://janusreit.com/role/COVERPAGE" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressesTable_019e183d-345f-7584-9341-eb19c96b9fa8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_EntityAddressesTable_019e183d-345f-7584-9341-eb19c96b9fa8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressesAddressTypeAxis_019e183d-345f-7f1f-8e94-44e349b4d44a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressesAddressTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_EntityAddressesTable_019e183d-345f-7584-9341-eb19c96b9fa8" xlink:to="loc_dei_EntityAddressesAddressTypeAxis_019e183d-345f-7f1f-8e94-44e349b4d44a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AddressTypeDomain_019e183d-345f-7f1f-8e94-44e349b4d44a_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AddressTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_EntityAddressesAddressTypeAxis_019e183d-345f-7f1f-8e94-44e349b4d44a" xlink:to="loc_dei_AddressTypeDomain_019e183d-345f-7f1f-8e94-44e349b4d44a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AddressTypeDomain_019e183d-345f-731d-881f-480a0f6ad8f5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AddressTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_EntityAddressesAddressTypeAxis_019e183d-345f-7f1f-8e94-44e349b4d44a" xlink:to="loc_dei_AddressTypeDomain_019e183d-345f-731d-881f-480a0f6ad8f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_FormerAddressMember_019e183d-345f-7c9b-b65f-3ede3b41efb5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_FormerAddressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_AddressTypeDomain_019e183d-345f-731d-881f-480a0f6ad8f5" xlink:to="loc_dei_FormerAddressMember_019e183d-345f-7c9b-b65f-3ede3b41efb5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019e183d-345f-76f9-abc9-cf977f2875ac" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_DocumentType_019e183d-345f-76f9-abc9-cf977f2875ac" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019e183d-345f-79a4-bb14-bfff73df440f" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_DocumentPeriodEndDate_019e183d-345f-79a4-bb14-bfff73df440f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019e183d-345f-75b0-beb6-a71110c9b657" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_EntityRegistrantName_019e183d-345f-75b0-beb6-a71110c9b657" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019e183d-345f-7360-bf87-1b71988851ad" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019e183d-345f-7360-bf87-1b71988851ad" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019e183d-345f-7c86-a972-97db7291dbd3" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_EntityFileNumber_019e183d-345f-7c86-a972-97db7291dbd3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019e183d-345f-7129-b70d-4b1f2fd967d3" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_EntityTaxIdentificationNumber_019e183d-345f-7129-b70d-4b1f2fd967d3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019e183d-345f-79bb-b4bc-59fc3ac9d5e2" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_EntityAddressAddressLine1_019e183d-345f-79bb-b4bc-59fc3ac9d5e2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_019e183d-345f-79ed-bbda-41084e882013" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_EntityAddressAddressLine2_019e183d-345f-79ed-bbda-41084e882013" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019e183d-345f-75bf-b847-8ee4e1b2fba3" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_EntityAddressCityOrTown_019e183d-345f-75bf-b847-8ee4e1b2fba3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019e183d-345f-7974-b314-aa21baf36b33" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_EntityAddressStateOrProvince_019e183d-345f-7974-b314-aa21baf36b33" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019e183d-345f-7bd3-8b32-9603ffc0921f" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_EntityAddressPostalZipCode_019e183d-345f-7bd3-8b32-9603ffc0921f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019e183d-345f-705d-8cb7-1bbecbfc81f4" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_CityAreaCode_019e183d-345f-705d-8cb7-1bbecbfc81f4" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019e183d-345f-7a1b-8750-f8dc5e5a2110" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_LocalPhoneNumber_019e183d-345f-7a1b-8750-f8dc5e5a2110" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019e183d-345f-7779-af36-4933fc82d81d" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_Security12bTitle_019e183d-345f-7779-af36-4933fc82d81d" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019e183d-345f-7d63-9b30-bf16b824f914" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_TradingSymbol_019e183d-345f-7d63-9b30-bf16b824f914" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019e183d-345f-7339-8610-b51e85823f36" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_SecurityExchangeName_019e183d-345f-7339-8610-b51e85823f36" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_019e183d-345f-765f-929a-5b8354926eff" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_WrittenCommunications_019e183d-345f-765f-929a-5b8354926eff" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_019e183d-345f-74ef-aa68-e157994850a9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_SolicitingMaterial_019e183d-345f-74ef-aa68-e157994850a9" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_019e183d-345f-7637-8f29-1681bb1441d0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_PreCommencementTenderOffer_019e183d-345f-7637-8f29-1681bb1441d0" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_019e183d-345f-7f54-9004-40c5d3985c76" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_019e183d-345f-7f54-9004-40c5d3985c76" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019e183d-345f-7593-a34e-05f433158d5a" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_EntityEmergingGrowthCompany_019e183d-345f-7593-a34e-05f433158d5a" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityExTransitionPeriod_019e183d-345f-7707-a1ff-3602e5881edc" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_EntityExTransitionPeriod_019e183d-345f-7707-a1ff-3602e5881edc" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019e183d-345f-7638-bcc9-396ba52c31d7" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_EntityCentralIndexKey_019e183d-345f-7638-bcc9-396ba52c31d7" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019e183d-345f-7a90-aad0-e0937de95f40" 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_EntityAddressesLineItems_019e183d-345f-7412-a1c4-ed0a72a2c8dc" xlink:to="loc_dei_AmendmentFlag_019e183d-345f-7a90-aad0-e0937de95f40" xlink:type="arc" order="23"/>
  </link:definitionLink>
</link:linkbase>
