<?xml version="1.0" encoding="us-ascii"?>
<!-- XBRL document created with Praxa -->
<!-- Copyright (c) 2026 Praxa LLC. All Rights Reserved.-->
<!-- Creation Date: 2026-08-13T00:55:30.9357+00:00 -->
<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" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#Cover" roleURI="http://onch.com/20260630/role/Cover" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#CondensedBalanceSheets" roleURI="http://onch.com/20260630/role/CondensedBalanceSheets" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#CondensedBalanceSheetsParentheticals" roleURI="http://onch.com/20260630/role/CondensedBalanceSheetsParentheticals" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#CondensedStatementsofOperationsUnaudited" roleURI="http://onch.com/20260630/role/CondensedStatementsofOperationsUnaudited" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#CondensedStatementsofChangesinShareholdersDeficitUnaudited" roleURI="http://onch.com/20260630/role/CondensedStatementsofChangesinShareholdersDeficitUnaudited" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#CondensedStatementsofCashFlowsUnaudited" roleURI="http://onch.com/20260630/role/CondensedStatementsofCashFlowsUnaudited" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#DescriptionofOrganizationandBusinessOperations" roleURI="http://onch.com/20260630/role/DescriptionofOrganizationandBusinessOperations" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#SummaryofSignificantAccountingPolicies" roleURI="http://onch.com/20260630/role/SummaryofSignificantAccountingPolicies" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#InitialPublicOffering" roleURI="http://onch.com/20260630/role/InitialPublicOffering" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#PrivatePlacement" roleURI="http://onch.com/20260630/role/PrivatePlacement" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#RelatedPartyTransactions" roleURI="http://onch.com/20260630/role/RelatedPartyTransactions" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#CommitmentsandContingency" roleURI="http://onch.com/20260630/role/CommitmentsandContingency" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#ShareholdersDeficit" roleURI="http://onch.com/20260630/role/ShareholdersDeficit" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#FairValueMeasurements" roleURI="http://onch.com/20260630/role/FairValueMeasurements" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#SegmentInformation" roleURI="http://onch.com/20260630/role/SegmentInformation" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#SubsequentEvents" roleURI="http://onch.com/20260630/role/SubsequentEvents" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#SummaryofSignificantAccountingPoliciesPolicies" roleURI="http://onch.com/20260630/role/SummaryofSignificantAccountingPoliciesPolicies" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#SummaryofSignificantAccountingPoliciesTables" roleURI="http://onch.com/20260630/role/SummaryofSignificantAccountingPoliciesTables" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#FairValueMeasurementsTables" roleURI="http://onch.com/20260630/role/FairValueMeasurementsTables" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#SegmentInformationTables" roleURI="http://onch.com/20260630/role/SegmentInformationTables" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#DescriptionofOrganizationandBusinessOperationsDetails" roleURI="http://onch.com/20260630/role/DescriptionofOrganizationandBusinessOperationsDetails" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#SummaryofSignificantAccountingPoliciesDetails" roleURI="http://onch.com/20260630/role/SummaryofSignificantAccountingPoliciesDetails" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#SummaryofSignificantAccountingPoliciesScheduleofClassAOrdinarySharesSubjecttoPossibleRedemptionDetails" roleURI="http://onch.com/20260630/role/SummaryofSignificantAccountingPoliciesScheduleofClassAOrdinarySharesSubjecttoPossibleRedemptionDetails" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#SummaryofSignificantAccountingPoliciesScheduleofBasicandDilutedNetIncomeLossPerOrdinaryShareDetails" roleURI="http://onch.com/20260630/role/SummaryofSignificantAccountingPoliciesScheduleofBasicandDilutedNetIncomeLossPerOrdinaryShareDetails" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#InitialPublicOfferingDetails" roleURI="http://onch.com/20260630/role/InitialPublicOfferingDetails" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#PrivatePlacementDetails" roleURI="http://onch.com/20260630/role/PrivatePlacementDetails" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#RelatedPartyTransactionsDetails" roleURI="http://onch.com/20260630/role/RelatedPartyTransactionsDetails" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#CommitmentsandContingencyDetails" roleURI="http://onch.com/20260630/role/CommitmentsandContingencyDetails" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#ShareholdersDeficitDetails" roleURI="http://onch.com/20260630/role/ShareholdersDeficitDetails" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#FairValueMeasurementsDetails" roleURI="http://onch.com/20260630/role/FairValueMeasurementsDetails" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#FairValueMeasurementsScheduleofCompanysAssetsThatareMeasuredatFairValueonaRecurringBasisDetails" roleURI="http://onch.com/20260630/role/FairValueMeasurementsScheduleofCompanysAssetsThatareMeasuredatFairValueonaRecurringBasisDetails" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#SegmentInformationDetails" roleURI="http://onch.com/20260630/role/SegmentInformationDetails" />
  <link:roleRef xlink:type="simple" xlink:href="onch-20260630.xsd#SegmentInformationScheduleofPerformanceandMakingKeyDecisionsRegardingResourceAllocationDetails" roleURI="http://onch.com/20260630/role/SegmentInformationScheduleofPerformanceandMakingKeyDecisionsRegardingResourceAllocationDetails" />
  <link:roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#InsiderTradingArrangements" roleURI="http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements" />
  <link:presentationLink xlink:role="http://onch.com/20260630/role/SummaryofSignificantAccountingPoliciesDetails" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAccrued" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAccrued_33858" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_InvestmentMaturityDays" xlink:label="onch_InvestmentMaturityDays_33859" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountingPoliciesAbstract" xlink:label="us-gaap_AccountingPoliciesAbstract_33854" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_33855" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashEquivalentsAtCarryingValue_34170" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFDICInsuredAmount" xlink:label="us-gaap_CashFDICInsuredAmount_33856" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UnrecognizedTaxBenefits" xlink:label="us-gaap_UnrecognizedTaxBenefits_33857" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33854" xlink:to="us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAccrued_33858" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="15.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33854" xlink:to="onch_InvestmentMaturityDays_33859" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="16.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33854" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_33855" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="497.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33854" xlink:to="us-gaap_CashEquivalentsAtCarryingValue_34170" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33854" xlink:to="us-gaap_CashFDICInsuredAmount_33856" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33854" xlink:to="us-gaap_UnrecognizedTaxBenefits_33857" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/SummaryofSignificantAccountingPoliciesScheduleofClassAOrdinarySharesSubjecttoPossibleRedemptionDetails" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentOfFinancingAndStockIssuanceCosts" xlink:label="us-gaap_PaymentOfFinancingAndStockIssuanceCosts_34130" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceInitialPublicOffering" xlink:label="us-gaap_ProceedsFromIssuanceInitialPublicOffering_33868" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfWarrants" xlink:label="us-gaap_ProceedsFromIssuanceOfWarrants_33869" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOrSaleOfEquityAbstract" xlink:label="us-gaap_ProceedsFromIssuanceOrSaleOfEquityAbstract_33871" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityAbstract" xlink:label="us-gaap_TemporaryEquityAbstract_33861" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment" xlink:label="us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_33873" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent" xlink:label="us-gaap_TemporaryEquityCarryingAmountAttributableToParent_33874" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityNumberOfSharesRedemptionValueAndOtherDisclosuresAbstract" xlink:label="us-gaap_TemporaryEquityNumberOfSharesRedemptionValueAndOtherDisclosuresAbstract_33872" />
    <link:presentationArc xlink:type="arc" order="473.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ProceedsFromIssuanceOrSaleOfEquityAbstract_33871" xlink:to="us-gaap_PaymentOfFinancingAndStockIssuanceCosts_34130" preferredLabel="http://www.xbrl.org/2009/role/negatedLabel" />
    <link:presentationArc xlink:type="arc" order="298.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_TemporaryEquityAbstract_33861" xlink:to="us-gaap_ProceedsFromIssuanceInitialPublicOffering_33868" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ProceedsFromIssuanceOrSaleOfEquityAbstract_33871" xlink:to="us-gaap_ProceedsFromIssuanceOfWarrants_33869" preferredLabel="http://www.xbrl.org/2009/role/negatedLabel" />
    <link:presentationArc xlink:type="arc" order="299.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_TemporaryEquityAbstract_33861" xlink:to="us-gaap_ProceedsFromIssuanceOrSaleOfEquityAbstract_33871" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="303.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_TemporaryEquityNumberOfSharesRedemptionValueAndOtherDisclosuresAbstract_33872" xlink:to="us-gaap_TemporaryEquityAccretionToRedemptionValueAdjustment_33873" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="304.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_TemporaryEquityNumberOfSharesRedemptionValueAndOtherDisclosuresAbstract_33872" xlink:to="us-gaap_TemporaryEquityCarryingAmountAttributableToParent_33874" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="300.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_TemporaryEquityAbstract_33861" xlink:to="us-gaap_TemporaryEquityNumberOfSharesRedemptionValueAndOtherDisclosuresAbstract_33872" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/SummaryofSignificantAccountingPoliciesScheduleofBasicandDilutedNetIncomeLossPerOrdinaryShareDetails" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_ScheduleOfBasicAndDilutedNetIncomeLossPerOrdinaryShareAbstract" xlink:label="onch_ScheduleOfBasicAndDilutedNetIncomeLossPerOrdinaryShareAbstract_33876" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsAttributableToParentAbstract" xlink:label="us-gaap_IncomeLossFromContinuingOperationsAttributableToParentAbstract_33883" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_33884" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_33886" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis_33878" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_33889" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="us-gaap_EarningsPerShareDiluted_33891" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasicLineItems" xlink:label="us-gaap_EarningsPerShareBasicLineItems_33882" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_33887" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic" xlink:label="us-gaap_EarningsPerShareBasic_33890" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember" xlink:label="us-gaap_CommonClassBMember_33881" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember" xlink:label="us-gaap_CommonClassAMember_33880" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain_33879" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_ScheduleOfBasicAndDilutedNetIncomeLossPerOrdinaryShareDetailsTable" xlink:label="onch_ScheduleOfBasicAndDilutedNetIncomeLossPerOrdinaryShareDetailsTable_33877" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_33888" />
    <link:presentationArc xlink:type="arc" order="312.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_EarningsPerShareBasicLineItems_33882" xlink:to="us-gaap_IncomeLossFromContinuingOperationsAttributableToParentAbstract_33883" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="313.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_IncomeLossFromContinuingOperationsAttributableToParentAbstract_33883" xlink:to="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_33884" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="315.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_IncomeLossFromContinuingOperationsAttributableToParentAbstract_33883" xlink:to="us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_33886" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="307.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_ScheduleOfBasicAndDilutedNetIncomeLossPerOrdinaryShareDetailsTable_33877" xlink:to="us-gaap_StatementClassOfStockAxis_33878" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="318.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_33887" xlink:to="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_33889" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="320.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_33887" xlink:to="us-gaap_EarningsPerShareDiluted_33891" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="311.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_ScheduleOfBasicAndDilutedNetIncomeLossPerOrdinaryShareDetailsTable_33877" xlink:to="us-gaap_EarningsPerShareBasicLineItems_33882" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="316.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_EarningsPerShareBasicLineItems_33882" xlink:to="us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_33887" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="319.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_33887" xlink:to="us-gaap_EarningsPerShareBasic_33890" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="310.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_33879" xlink:to="us-gaap_CommonClassBMember_33881" preferredLabel="http://www.xbrl.org/2003/role/disclosureGuidance" />
    <link:presentationArc xlink:type="arc" order="309.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_33879" xlink:to="us-gaap_CommonClassAMember_33880" preferredLabel="http://www.xbrl.org/2003/role/disclosureGuidance" />
    <link:presentationArc xlink:type="arc" order="308.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementClassOfStockAxis_33878" xlink:to="us-gaap_ClassOfStockDomain_33879" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="306.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_ScheduleOfBasicAndDilutedNetIncomeLossPerOrdinaryShareAbstract_33876" xlink:to="onch_ScheduleOfBasicAndDilutedNetIncomeLossPerOrdinaryShareDetailsTable_33877" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="317.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_33887" xlink:to="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_33888" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/RelatedPartyTransactions" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsAbstract" xlink:label="us-gaap_RelatedPartyTransactionsAbstract_33893" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsDisclosureTextBlock" xlink:label="us-gaap_RelatedPartyTransactionsDisclosureTextBlock_33894" />
    <link:presentationArc xlink:type="arc" order="322.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionsAbstract_33893" xlink:to="us-gaap_RelatedPartyTransactionsDisclosureTextBlock_33894" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/RelatedPartyTransactionsDetails" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_FairValueOfFounderShares" xlink:label="onch_FairValueOfFounderShares_33936" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_FounderSharesMember" xlink:label="onch_FounderSharesMember_33916" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_FounderSharesMembershipInterestsHoldersValue" xlink:label="onch_FounderSharesMembershipInterestsHoldersValue_33937" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_NumberOfConsecutiveTradingDays" xlink:label="onch_NumberOfConsecutiveTradingDays_33924" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_NumberOfSharesNoLongerSubjectToForfeiture" xlink:label="onch_NumberOfSharesNoLongerSubjectToForfeiture_34150" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_RelatedPartyTransactionsTable" xlink:label="onch_RelatedPartyTransactionsTable_33897" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_SponsorMember" xlink:label="onch_SponsorMember_33900" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_WorkingCapitalLoansMember" xlink:label="onch_WorkingCapitalLoansMember_33934" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_DirectorMember" xlink:label="srt_DirectorMember_33914" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain_33933" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:label="us-gaap_DebtInstrumentFaceAmount_33930" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentAxis" xlink:label="us-gaap_DebtInstrumentAxis_33932" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember" xlink:label="us-gaap_CommonClassAMember_33919" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_33931" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain_33918" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="srt_TitleOfIndividualWithRelationshipToEntityDomain_33913" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfRelatedPartyDebt" xlink:label="us-gaap_RepaymentsOfRelatedPartyDebt_33925" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_33898" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsAbstract" xlink:label="us-gaap_RelatedPartyTransactionsAbstract_33896" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems" xlink:label="us-gaap_RelatedPartyTransactionLineItems_33901" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAmountsOfTransaction" xlink:label="us-gaap_RelatedPartyTransactionAmountsOfTransaction_33929" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain" xlink:label="us-gaap_RelatedPartyDomain_33899" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromRepaymentsOfDebt" xlink:label="us-gaap_ProceedsFromRepaymentsOfDebt_33926" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceInitialPublicOffering" xlink:label="us-gaap_ProceedsFromIssuanceInitialPublicOffering_33902" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForFees" xlink:label="us-gaap_PaymentsForFees_33938" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualAxis" xlink:label="srt_TitleOfIndividualAxis_33912" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember" xlink:label="srt_RangeMember_33921" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis_33920" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember_33923" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember_33922" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_WorkingCapitalLoanOutstanding" xlink:label="onch_WorkingCapitalLoanOutstanding_34181" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited" xlink:label="us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited_34166" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_33904" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis_33917" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesIssuedPricePerShare" xlink:label="us-gaap_SharesIssuedPricePerShare_33903" />
    <link:presentationArc xlink:type="arc" order="17.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionLineItems_33901" xlink:to="onch_FairValueOfFounderShares_33936" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="343.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyDomain_33899" xlink:to="onch_FounderSharesMember_33916" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="18.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionLineItems_33901" xlink:to="onch_FounderSharesMembershipInterestsHoldersValue_33937" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="19.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionLineItems_33901" xlink:to="onch_NumberOfConsecutiveTradingDays_33924" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="28.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionLineItems_33901" xlink:to="onch_NumberOfSharesNoLongerSubjectToForfeiture_34150" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="324.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionsAbstract_33896" xlink:to="onch_RelatedPartyTransactionsTable_33897" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="327.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyDomain_33899" xlink:to="onch_SponsorMember_33900" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="361.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_DebtInstrumentNameDomain_33933" xlink:to="onch_WorkingCapitalLoansMember_33934" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="341.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="srt_TitleOfIndividualWithRelationshipToEntityDomain_33913" xlink:to="srt_DirectorMember_33914" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="360.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_DebtInstrumentAxis_33932" xlink:to="us-gaap_DebtInstrumentNameDomain_33933" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="26.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionLineItems_33901" xlink:to="us-gaap_DebtInstrumentFaceAmount_33930" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="16.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_RelatedPartyTransactionsTable_33897" xlink:to="us-gaap_DebtInstrumentAxis_33932" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="346.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_33918" xlink:to="us-gaap_CommonClassAMember_33919" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="27.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionLineItems_33901" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_33931" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="345.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementClassOfStockAxis_33917" xlink:to="us-gaap_ClassOfStockDomain_33918" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="340.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="srt_TitleOfIndividualAxis_33912" xlink:to="srt_TitleOfIndividualWithRelationshipToEntityDomain_33913" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="20.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionLineItems_33901" xlink:to="us-gaap_RepaymentsOfRelatedPartyDebt_33925" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_RelatedPartyTransactionsTable_33897" xlink:to="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_33898" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="17.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_RelatedPartyTransactionsTable_33897" xlink:to="us-gaap_RelatedPartyTransactionLineItems_33901" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="24.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionLineItems_33901" xlink:to="us-gaap_RelatedPartyTransactionAmountsOfTransaction_33929" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="326.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_33898" xlink:to="us-gaap_RelatedPartyDomain_33899" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="21.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionLineItems_33901" xlink:to="us-gaap_ProceedsFromRepaymentsOfDebt_33926" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionLineItems_33901" xlink:to="us-gaap_ProceedsFromIssuanceInitialPublicOffering_33902" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="25.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionLineItems_33901" xlink:to="us-gaap_PaymentsForFees_33938" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_RelatedPartyTransactionsTable_33897" xlink:to="srt_TitleOfIndividualAxis_33912" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="348.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="srt_RangeAxis_33920" xlink:to="srt_RangeMember_33921" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="15.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_RelatedPartyTransactionsTable_33897" xlink:to="srt_RangeAxis_33920" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="350.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="srt_RangeMember_33921" xlink:to="srt_MinimumMember_33923" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="349.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="srt_RangeMember_33921" xlink:to="srt_MaximumMember_33922" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="507.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionLineItems_33901" xlink:to="onch_WorkingCapitalLoanOutstanding_34181" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="494.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionLineItems_33901" xlink:to="us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited_34166" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionLineItems_33901" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues_33904" preferredLabel="http://www.xbrl.org/2003/role/definitionGuidance" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_RelatedPartyTransactionsTable_33897" xlink:to="us-gaap_StatementClassOfStockAxis_33917" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionLineItems_33901" xlink:to="us-gaap_SharesIssuedPricePerShare_33903" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/ShareholdersDeficitDetails" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="us-gaap_PreferredStockSharesIssued_33990" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesOutstanding" xlink:label="us-gaap_PreferredStockSharesOutstanding_33991" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain" xlink:label="us-gaap_RelatedPartyDomain_33975" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_33974" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember" xlink:label="us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_33983" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_ClassOfWarrantOrRightRedemptionOfWarrantsOrRightsStockPriceTrigger" xlink:label="onch_ClassOfWarrantOrRightRedemptionOfWarrantsOrRightsStockPriceTrigger_34021" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_ClassOfWarrantOrRightExercisableEntityMayRedeemRedemptionWrittenNoticePeriod" xlink:label="onch_ClassOfWarrantOrRightExercisableEntityMayRedeemRedemptionWrittenNoticePeriod_34010" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain_33982" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis_33981" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired" xlink:label="us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_34003" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionSharePrice" xlink:label="us-gaap_BusinessAcquisitionSharePrice_34012" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain_33971" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesIssuedPricePerShare" xlink:label="us-gaap_SharesIssuedPricePerShare_33998" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis_33970" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis_33978" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityNoteAbstract" xlink:label="us-gaap_StockholdersEquityNoteAbstract_33966" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_33996" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited" xlink:label="us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited_34167" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockLineItems" xlink:label="us-gaap_ClassOfStockLineItems_33987" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis_33984" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain_33985" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_34005" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightOutstanding" xlink:label="us-gaap_ClassOfWarrantOrRightOutstanding_34004" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember" xlink:label="us-gaap_CommonClassAMember_33972" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember" xlink:label="us-gaap_CommonClassBMember_33973" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember_33980" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_33993" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="us-gaap_CommonStockSharesAuthorized_33992" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued" xlink:label="us-gaap_CommonStockSharesIssued_33994" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="us-gaap_CommonStockSharesOutstanding_34017" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockVotingRights" xlink:label="us-gaap_CommonStockVotingRights_34002" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain_33979" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockParOrStatedValuePerShare" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_33989" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="us-gaap_PreferredStockSharesAuthorized_33988" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_FounderSharesMember" xlink:label="onch_FounderSharesMember_33977" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_MaximumPeriodAfterBusinessCombinationInWhichToFileRegistrationStatement" xlink:label="onch_MaximumPeriodAfterBusinessCombinationInWhichToFileRegistrationStatement_34008" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_NumberOfSharesNoLongerSubjectToForfeiture" xlink:label="onch_NumberOfSharesNoLongerSubjectToForfeiture_34000" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_NumberOfTradingDays" xlink:label="onch_NumberOfTradingDays_34011" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_NumberOfTradingDaysCommencing" xlink:label="onch_NumberOfTradingDaysCommencing_34018" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_NumberOfTradingDaysCompletion" xlink:label="onch_NumberOfTradingDaysCompletion_34019" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_PercentageOfConversionOfOrdinaryShares" xlink:label="onch_PercentageOfConversionOfOrdinaryShares_34001" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_PercentageOfNewlyIssuedShares" xlink:label="onch_PercentageOfNewlyIssuedShares_34132" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_PeriodOfTimeWithInWhichRegistrationStatementIsExpectedToBecomeEffective" xlink:label="onch_PeriodOfTimeWithInWhichRegistrationStatementIsExpectedToBecomeEffective_34009" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_PublicWarrantsMember" xlink:label="onch_PublicWarrantsMember_33986" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_RedemptionPeriod" xlink:label="onch_RedemptionPeriod_34022" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_ShareholdersDeficitEquityDetailsTable" xlink:label="onch_ShareholdersDeficitEquityDetailsTable_33967" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_SponsorMember" xlink:label="onch_SponsorMember_33976" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_WarrantsAndRightsOutstandingExercisableTermAfterBusinessCombination" xlink:label="onch_WarrantsAndRightsOutstandingExercisableTermAfterBusinessCombination_34007" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember_34136" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember_34135" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis_34133" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember" xlink:label="srt_RangeMember_34134" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstandingTerm" xlink:label="us-gaap_WarrantsAndRightsOutstandingTerm_34006" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesIssued" xlink:label="us-gaap_TemporaryEquitySharesIssued_33995" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues_33997" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_PreferredStockSharesIssued_33990" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_PreferredStockSharesOutstanding_33991" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_33974" xlink:to="us-gaap_RelatedPartyDomain_33975" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_ShareholdersDeficitEquityDetailsTable_33967" xlink:to="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_33974" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="390.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain_33982" xlink:to="us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_33983" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="39.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="onch_ClassOfWarrantOrRightRedemptionOfWarrantsOrRightsStockPriceTrigger_34021" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="34.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="onch_ClassOfWarrantOrRightExercisableEntityMayRedeemRedemptionWrittenNoticePeriod_34010" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="389.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_BusinessAcquisitionAxis_33981" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain_33982" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_ShareholdersDeficitEquityDetailsTable_33967" xlink:to="us-gaap_BusinessAcquisitionAxis_33981" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="27.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_34003" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="41.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_BusinessAcquisitionSharePrice_34012" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementClassOfStockAxis_33970" xlink:to="us-gaap_ClassOfStockDomain_33971" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="22.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_SharesIssuedPricePerShare_33998" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_ShareholdersDeficitEquityDetailsTable_33967" xlink:to="us-gaap_StatementClassOfStockAxis_33970" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_ShareholdersDeficitEquityDetailsTable_33967" xlink:to="us-gaap_StatementEquityComponentsAxis_33978" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="20.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues_33996" preferredLabel="http://www.xbrl.org/2003/role/disclosureGuidance" />
    <link:presentationArc xlink:type="arc" order="476.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationForfeited_34167" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="18.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_ShareholdersDeficitEquityDetailsTable_33967" xlink:to="us-gaap_ClassOfStockLineItems_33987" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="15.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_ShareholdersDeficitEquityDetailsTable_33967" xlink:to="us-gaap_ClassOfWarrantOrRightAxis_33984" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="392.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfWarrantOrRightAxis_33984" xlink:to="us-gaap_ClassOfWarrantOrRightDomain_33985" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="29.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_34005" preferredLabel="http://www.xbrl.org/2003/role/definitionGuidance" />
    <link:presentationArc xlink:type="arc" order="28.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_ClassOfWarrantOrRightOutstanding_34004" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_33971" xlink:to="us-gaap_CommonClassAMember_33972" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_33971" xlink:to="us-gaap_CommonClassBMember_33973" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_EquityComponentDomain_33979" xlink:to="us-gaap_CommonStockMember_33980" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="16.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare_33993" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="15.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_CommonStockSharesAuthorized_33992" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="17.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_CommonStockSharesIssued_33994" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="18.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_CommonStockSharesOutstanding_34017" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="26.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_CommonStockVotingRights_34002" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementEquityComponentsAxis_33978" xlink:to="us-gaap_EquityComponentDomain_33979" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_PreferredStockParOrStatedValuePerShare_33989" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_PreferredStockSharesAuthorized_33988" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyDomain_33975" xlink:to="onch_FounderSharesMember_33977" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="32.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="onch_MaximumPeriodAfterBusinessCombinationInWhichToFileRegistrationStatement_34008" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="24.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="onch_NumberOfSharesNoLongerSubjectToForfeiture_34000" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="35.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="onch_NumberOfTradingDays_34011" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="36.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="onch_NumberOfTradingDaysCommencing_34018" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="37.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="onch_NumberOfTradingDaysCompletion_34019" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="25.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="onch_PercentageOfConversionOfOrdinaryShares_34001" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="475.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="onch_PercentageOfNewlyIssuedShares_34132" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="33.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="onch_PeriodOfTimeWithInWhichRegistrationStatementIsExpectedToBecomeEffective_34009" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="393.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfWarrantOrRightDomain_33985" xlink:to="onch_PublicWarrantsMember_33986" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="40.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="onch_RedemptionPeriod_34022" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="387.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StockholdersEquityNoteAbstract_33966" xlink:to="onch_ShareholdersDeficitEquityDetailsTable_33967" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyDomain_33975" xlink:to="onch_SponsorMember_33976" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="30.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="onch_WarrantsAndRightsOutstandingExercisableTermAfterBusinessCombination_34007" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="479.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="srt_RangeMember_34134" xlink:to="srt_MaximumMember_34136" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="478.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="srt_RangeMember_34134" xlink:to="srt_MinimumMember_34135" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="16.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_ShareholdersDeficitEquityDetailsTable_33967" xlink:to="srt_RangeAxis_34133" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="477.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="srt_RangeAxis_34133" xlink:to="srt_RangeMember_34134" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="31.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_WarrantsAndRightsOutstandingTerm_34006" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="19.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_TemporaryEquitySharesIssued_33995" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="21.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33987" xlink:to="us-gaap_StockIssuedDuringPeriodValueNewIssues_33997" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/ShareholdersDeficit" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityNoteDisclosureTextBlock" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock_33964" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityNoteAbstract" xlink:label="us-gaap_StockholdersEquityNoteAbstract_33963" />
    <link:presentationArc xlink:type="arc" order="385.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StockholdersEquityNoteAbstract_33963" xlink:to="us-gaap_StockholdersEquityNoteDisclosureTextBlock_33964" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/CommitmentsandContingencyDetails" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="us-gaap_TypeOfArrangementAxis_33949" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_33945" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharePrice" xlink:label="us-gaap_SharePrice_33956" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_33946" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromStockOptionsExercised" xlink:label="us-gaap_ProceedsFromStockOptionsExercised_33961" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OverAllotmentOptionMember" xlink:label="us-gaap_OverAllotmentOptionMember_33948" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherCommitmentsLineItems" xlink:label="us-gaap_OtherCommitmentsLineItems_33953" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IPOMember" xlink:label="us-gaap_IPOMember_33947" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingenciesDisclosureAbstract" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureAbstract_33943" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_33950" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_UnitsIssuedDuringPeriodSharesNewIssues" xlink:label="onch_UnitsIssuedDuringPeriodSharesNewIssues_33955" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_UnderwritingDiscountGrossProceedsPercentage" xlink:label="onch_UnderwritingDiscountGrossProceedsPercentage_33960" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_UnderwritersOptionFromProposedPublicOffering" xlink:label="onch_UnderwritersOptionFromProposedPublicOffering_33954" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_UnderwritersAgreementMember" xlink:label="onch_UnderwritersAgreementMember_33952" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_UnderwriterCashDiscount" xlink:label="onch_UnderwriterCashDiscount_33957" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_DeferredUnderwritingDiscount" xlink:label="onch_DeferredUnderwritingDiscount_33959" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_CommitmentsAndContingencyDetailsTable" xlink:label="onch_CommitmentsAndContingencyDetailsTable_33944" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_CashUnderwritingDiscountRate" xlink:label="onch_CashUnderwritingDiscountRate_33958" />
    <link:presentationArc xlink:type="arc" order="371.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_CommitmentsAndContingencyDetailsTable_33944" xlink:to="us-gaap_TypeOfArrangementAxis_33949" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="367.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_CommitmentsAndContingencyDetailsTable_33944" xlink:to="us-gaap_SubsidiarySaleOfStockAxis_33945" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="378.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_OtherCommitmentsLineItems_33953" xlink:to="us-gaap_SharePrice_33956" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="368.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SubsidiarySaleOfStockAxis_33945" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain_33946" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="383.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_OtherCommitmentsLineItems_33953" xlink:to="us-gaap_ProceedsFromStockOptionsExercised_33961" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="370.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain_33946" xlink:to="us-gaap_OverAllotmentOptionMember_33948" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="375.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_CommitmentsAndContingencyDetailsTable_33944" xlink:to="us-gaap_OtherCommitmentsLineItems_33953" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="369.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain_33946" xlink:to="us-gaap_IPOMember_33947" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="372.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_TypeOfArrangementAxis_33949" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember_33950" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="377.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_OtherCommitmentsLineItems_33953" xlink:to="onch_UnitsIssuedDuringPeriodSharesNewIssues_33955" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="382.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_OtherCommitmentsLineItems_33953" xlink:to="onch_UnderwritingDiscountGrossProceedsPercentage_33960" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="376.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_OtherCommitmentsLineItems_33953" xlink:to="onch_UnderwritersOptionFromProposedPublicOffering_33954" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="374.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ArrangementsAndNonarrangementTransactionsMember_33950" xlink:to="onch_UnderwritersAgreementMember_33952" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="379.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_OtherCommitmentsLineItems_33953" xlink:to="onch_UnderwriterCashDiscount_33957" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="381.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_OtherCommitmentsLineItems_33953" xlink:to="onch_DeferredUnderwritingDiscount_33959" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="366.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CommitmentsAndContingenciesDisclosureAbstract_33943" xlink:to="onch_CommitmentsAndContingencyDetailsTable_33944" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="380.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_OtherCommitmentsLineItems_33953" xlink:to="onch_CashUnderwritingDiscountRate_33958" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/CondensedStatementsofOperationsUnaudited" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems_1048" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable_1047" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_1055" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_1054" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeStatementAbstract" xlink:label="us-gaap_IncomeStatementAbstract_1046" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralAndAdministrativeExpense" xlink:label="us-gaap_GeneralAndAdministrativeExpense_1049" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="us-gaap_EarningsPerShareDiluted_1077" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic" xlink:label="us-gaap_EarningsPerShareBasic_1076" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember" xlink:label="us-gaap_CommonClassBMember_1062" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain_1060" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember" xlink:label="us-gaap_CommonClassAMember_34157" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense" xlink:label="us-gaap_NonoperatingIncomeExpense_1052" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpenseAbstract" xlink:label="us-gaap_NonoperatingIncomeExpenseAbstract_33607" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInterest" xlink:label="us-gaap_InvestmentIncomeInterest_1051" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss_34154" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss" xlink:label="us-gaap_OperatingIncomeLoss_34153" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis_1059" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_InterestEarnedOnCashHeldInOperatingBankAccount" xlink:label="onch_InterestEarnedOnCashHeldInOperatingBankAccount_34171" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementTable_1047" xlink:to="us-gaap_StatementLineItems_1048" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="55.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_IncomeStatementAbstract_1046" xlink:to="us-gaap_StatementTable_1047" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="15.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_1048" xlink:to="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_1055" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_1048" xlink:to="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_1054" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_1048" xlink:to="us-gaap_GeneralAndAdministrativeExpense_1049" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="17.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_1048" xlink:to="us-gaap_EarningsPerShareDiluted_1077" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="16.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_1048" xlink:to="us-gaap_EarningsPerShareBasic_1076" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_1060" xlink:to="us-gaap_CommonClassBMember_1062" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="66.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementClassOfStockAxis_1059" xlink:to="us-gaap_ClassOfStockDomain_1060" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_1060" xlink:to="us-gaap_CommonClassAMember_34157" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract_33607" xlink:to="us-gaap_NonoperatingIncomeExpense_1052" preferredLabel="http://www.xbrl.org/2003/role/totalLabel" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_1048" xlink:to="us-gaap_NonoperatingIncomeExpenseAbstract_33607" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract_33607" xlink:to="us-gaap_InvestmentIncomeInterest_1051" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract_33607" xlink:to="us-gaap_NetIncomeLoss_34154" preferredLabel="http://www.xbrl.org/2003/role/totalLabel" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_1048" xlink:to="us-gaap_OperatingIncomeLoss_34153" preferredLabel="http://www.xbrl.org/2003/role/totalLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementTable_1047" xlink:to="us-gaap_StatementClassOfStockAxis_1059" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract_33607" xlink:to="onch_InterestEarnedOnCashHeldInOperatingBankAccount_34171" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/CondensedBalanceSheets" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable_33587" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfFinancialPositionAbstract" xlink:label="us-gaap_StatementOfFinancialPositionAbstract_33586" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems_33590" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis_33634" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_33628" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_33603" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities" xlink:label="us-gaap_Liabilities_33612" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseCurrent" xlink:label="us-gaap_PrepaidExpenseCurrent_33595" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue" xlink:label="us-gaap_CommonStockValue_33625" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="us-gaap_CommitmentsAndContingencies_33613" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsHeldInTrustNoncurrent" xlink:label="us-gaap_AssetsHeldInTrustNoncurrent_33599" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets" xlink:label="us-gaap_Assets_33601" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="us-gaap_AdditionalPaidInCapital_33626" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain_33635" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_33593" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="us-gaap_AssetsCurrentAbstract_33592" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract" xlink:label="us-gaap_AssetsAbstract_33591" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseNoncurrent" xlink:label="us-gaap_PrepaidExpenseNoncurrent_33598" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember" xlink:label="us-gaap_CommonClassBMember_33639" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember" xlink:label="us-gaap_CommonClassAMember_33636" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_33630" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="us-gaap_LiabilitiesCurrentAbstract_33605" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockValue" xlink:label="us-gaap_PreferredStockValue_33624" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_AccruedOfferingCosts" xlink:label="onch_AccruedOfferingCosts_33608" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="us-gaap_AccruedLiabilitiesCurrent_33606" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent" xlink:label="us-gaap_TemporaryEquityCarryingAmountAttributableToParent_33622" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="us-gaap_StockholdersEquityAbstract_33623" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity_33629" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent" xlink:label="us-gaap_LiabilitiesCurrent_33610" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredCompensationLiabilityClassifiedNoncurrent" xlink:label="us-gaap_DeferredCompensationLiabilityClassifiedNoncurrent_33611" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrent" xlink:label="us-gaap_AssetsCurrent_33596" />
    <link:presentationArc xlink:type="arc" order="88.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementOfFinancialPositionAbstract_33586" xlink:to="us-gaap_StatementTable_33587" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementTable_33587" xlink:to="us-gaap_StatementLineItems_33590" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementTable_33587" xlink:to="us-gaap_StatementClassOfStockAxis_33634" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="127.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StockholdersEquityAbstract_33623" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit_33628" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="104.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33590" xlink:to="us-gaap_LiabilitiesAndStockholdersEquityAbstract_33603" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="113.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract_33603" xlink:to="us-gaap_Liabilities_33612" preferredLabel="http://www.xbrl.org/2003/role/totalLabel" />
    <link:presentationArc xlink:type="arc" order="96.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AssetsCurrentAbstract_33592" xlink:to="us-gaap_PrepaidExpenseCurrent_33595" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="124.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StockholdersEquityAbstract_33623" xlink:to="us-gaap_CommonStockValue_33625" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="114.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract_33603" xlink:to="us-gaap_CommitmentsAndContingencies_33613" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="100.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AssetsAbstract_33591" xlink:to="us-gaap_AssetsHeldInTrustNoncurrent_33599" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="102.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AssetsAbstract_33591" xlink:to="us-gaap_Assets_33601" preferredLabel="http://www.xbrl.org/2003/role/totalLabel" />
    <link:presentationArc xlink:type="arc" order="125.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StockholdersEquityAbstract_33623" xlink:to="us-gaap_AdditionalPaidInCapital_33626" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="134.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementClassOfStockAxis_33634" xlink:to="us-gaap_ClassOfStockDomain_33635" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="94.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AssetsCurrentAbstract_33592" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_33593" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="93.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AssetsAbstract_33591" xlink:to="us-gaap_AssetsCurrentAbstract_33592" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="92.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33590" xlink:to="us-gaap_AssetsAbstract_33591" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="99.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AssetsAbstract_33591" xlink:to="us-gaap_PrepaidExpenseNoncurrent_33598" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="138.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_33635" xlink:to="us-gaap_CommonClassBMember_33639" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="135.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_33635" xlink:to="us-gaap_CommonClassAMember_33636" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="129.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract_33603" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity_33630" preferredLabel="http://www.xbrl.org/2003/role/totalLabel" />
    <link:presentationArc xlink:type="arc" order="106.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract_33603" xlink:to="us-gaap_LiabilitiesCurrentAbstract_33605" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="123.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StockholdersEquityAbstract_33623" xlink:to="us-gaap_PreferredStockValue_33624" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="109.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_LiabilitiesCurrentAbstract_33605" xlink:to="onch_AccruedOfferingCosts_33608" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="107.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_LiabilitiesCurrentAbstract_33605" xlink:to="us-gaap_AccruedLiabilitiesCurrent_33606" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="121.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract_33603" xlink:to="us-gaap_TemporaryEquityCarryingAmountAttributableToParent_33622" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="122.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract_33603" xlink:to="us-gaap_StockholdersEquityAbstract_33623" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="128.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StockholdersEquityAbstract_33623" xlink:to="us-gaap_StockholdersEquity_33629" preferredLabel="http://www.xbrl.org/2003/role/totalLabel" />
    <link:presentationArc xlink:type="arc" order="111.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_LiabilitiesCurrentAbstract_33605" xlink:to="us-gaap_LiabilitiesCurrent_33610" preferredLabel="http://www.xbrl.org/2003/role/totalLabel" />
    <link:presentationArc xlink:type="arc" order="112.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract_33603" xlink:to="us-gaap_DeferredCompensationLiabilityClassifiedNoncurrent_33611" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="97.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AssetsCurrentAbstract_33592" xlink:to="us-gaap_AssetsCurrent_33596" preferredLabel="http://www.xbrl.org/2003/role/totalLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/Cover" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember" xlink:label="us-gaap_CommonClassBMember_1044" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitySmallBusiness" xlink:label="dei_EntitySmallBusiness_1023" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_Security12bTitle" xlink:label="dei_Security12bTitle_1036" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber" xlink:label="dei_LocalPhoneNumber_1034" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey" xlink:label="dei_EntityCentralIndexKey_1013" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince" xlink:label="dei_EntityAddressStateOrProvince_1030" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode" xlink:label="dei_EntityAddressPostalZipCode_1032" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown" xlink:label="dei_EntityAddressCityOrTown_34124" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine2" xlink:label="dei_EntityAddressAddressLine2_1028" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1" xlink:label="dei_EntityAddressAddressLine1_1027" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType" xlink:label="dei_DocumentType_1005" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentTransitionReport" xlink:label="dei_DocumentTransitionReport_1039" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentQuarterlyReport" xlink:label="dei_DocumentQuarterlyReport_34158" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate" xlink:label="dei_DocumentPeriodEndDate_1010" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationTable" xlink:label="dei_DocumentInformationTable_1003" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationLineItems" xlink:label="dei_DocumentInformationLineItems_1004" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalYearFocus" xlink:label="dei_DocumentFiscalYearFocus_1011" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalPeriodFocus" xlink:label="dei_DocumentFiscalPeriodFocus_1012" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember" xlink:label="us-gaap_CommonClassAMember_1043" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber" xlink:label="dei_EntityTaxIdentificationNumber_1016" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SecurityExchangeName" xlink:label="dei_SecurityExchangeName_1037" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_TradingSymbol" xlink:label="dei_TradingSymbol_1035" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_ClassAOrdinarySharesParValue00001PerShareMember" xlink:label="onch_ClassAOrdinarySharesParValue00001PerShareMember_1057" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain_1042" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis_1041" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CurrentFiscalYearEndDate" xlink:label="dei_CurrentFiscalYearEndDate_1040" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CoverAbstract" xlink:label="dei_CoverAbstract_1002" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode" xlink:label="dei_CityAreaCode_1033" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag" xlink:label="dei_AmendmentFlag_1078" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCommonStockSharesOutstanding" xlink:label="dei_EntityCommonStockSharesOutstanding_1038" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCurrentReportingStatus" xlink:label="dei_EntityCurrentReportingStatus_1020" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany" xlink:label="dei_EntityEmergingGrowthCompany_1024" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityExTransitionPeriod" xlink:label="dei_EntityExTransitionPeriod_1025" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber" xlink:label="dei_EntityFileNumber_1015" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFilerCategory" xlink:label="dei_EntityFilerCategory_1022" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode" xlink:label="dei_EntityIncorporationStateCountryCode_1017" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInteractiveDataCurrent" xlink:label="dei_EntityInteractiveDataCurrent_1008" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName" xlink:label="dei_EntityRegistrantName_1014" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityShellCompany" xlink:label="dei_EntityShellCompany_1021" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_UnitsEachConsistingOfOneClassAOrdinaryShareAndOnequarterOfOneRedeemableWarrantMember" xlink:label="onch_UnitsEachConsistingOfOneClassAOrdinaryShareAndOnequarterOfOneRedeemableWarrantMember_1056" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_WarrantsEachWholeWarrantExercisableForOneClassAOrdinaryShareAtAnExercisePriceOf1150PerShareMember" xlink:label="onch_WarrantsEachWholeWarrantExercisableForOneClassAOrdinaryShareAtAnExercisePriceOf1150PerShareMember_34152" />
    <link:presentationArc xlink:type="arc" order="53.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_1042" xlink:to="us-gaap_CommonClassBMember_1044" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="28.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntitySmallBusiness_1023" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="38.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_Security12bTitle_1036" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="37.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_LocalPhoneNumber_1034" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="20.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityCentralIndexKey_1013" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="34.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityAddressStateOrProvince_1030" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="35.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityAddressPostalZipCode_1032" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="33.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityAddressCityOrTown_34124" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="32.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityAddressAddressLine2_1028" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="31.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityAddressAddressLine1_1027" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_DocumentType_1005" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_DocumentTransitionReport_1039" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_DocumentQuarterlyReport_34158" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="16.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_DocumentPeriodEndDate_1010" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_CoverAbstract_1002" xlink:to="dei_DocumentInformationTable_1003" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationTable_1003" xlink:to="dei_DocumentInformationLineItems_1004" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="17.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_DocumentFiscalYearFocus_1011" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="18.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_DocumentFiscalPeriodFocus_1012" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="52.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_1042" xlink:to="us-gaap_CommonClassAMember_1043" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="22.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityTaxIdentificationNumber_1016" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="40.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_SecurityExchangeName_1037" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="39.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_TradingSymbol_1035" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="55.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_1042" xlink:to="onch_ClassAOrdinarySharesParValue00001PerShareMember_1057" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="51.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementClassOfStockAxis_1041" xlink:to="us-gaap_ClassOfStockDomain_1042" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationTable_1003" xlink:to="us-gaap_StatementClassOfStockAxis_1041" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="24.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_CurrentFiscalYearEndDate_1040" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="36.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_CityAreaCode_1033" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="15.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_AmendmentFlag_1078" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="41.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityCommonStockSharesOutstanding_1038" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="25.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityCurrentReportingStatus_1020" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="29.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityEmergingGrowthCompany_1024" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="30.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityExTransitionPeriod_1025" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="21.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityFileNumber_1015" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="27.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityFilerCategory_1022" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="23.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityIncorporationStateCountryCode_1017" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityInteractiveDataCurrent_1008" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="19.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityRegistrantName_1014" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="26.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="dei_DocumentInformationLineItems_1004" xlink:to="dei_EntityShellCompany_1021" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="54.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_1042" xlink:to="onch_UnitsEachConsistingOfOneClassAOrdinaryShareAndOnequarterOfOneRedeemableWarrantMember_1056" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="486.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_1042" xlink:to="onch_WarrantsEachWholeWarrantExercisableForOneClassAOrdinaryShareAtAnExercisePriceOf1150PerShareMember_34152" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/CondensedBalanceSheetsParentheticals" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain_33663" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember" xlink:label="us-gaap_CommonClassAMember_33664" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember" xlink:label="us-gaap_CommonClassBMember_33665" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="us-gaap_PreferredStockSharesAuthorized_33677" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockParOrStatedValuePerShare" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_33676" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="us-gaap_CommonStockSharesOutstanding_34125" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued" xlink:label="us-gaap_CommonStockSharesIssued_33682" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="us-gaap_CommonStockSharesAuthorized_33681" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_33680" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="us-gaap_PreferredStockSharesIssued_33678" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable_33661" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfFinancialPositionAbstract" xlink:label="us-gaap_StatementOfFinancialPositionAbstract_33660" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems_33671" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis_33662" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesOutstanding" xlink:label="us-gaap_PreferredStockSharesOutstanding_33679" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityRedemptionPricePerShare" xlink:label="us-gaap_TemporaryEquityRedemptionPricePerShare_33674" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesIssued" xlink:label="us-gaap_TemporaryEquitySharesIssued_33673" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquitySharesOutstanding" xlink:label="us-gaap_TemporaryEquitySharesOutstanding_33720" />
    <link:presentationArc xlink:type="arc" order="161.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementClassOfStockAxis_33662" xlink:to="us-gaap_ClassOfStockDomain_33663" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="162.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_33663" xlink:to="us-gaap_CommonClassAMember_33664" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="163.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_33663" xlink:to="us-gaap_CommonClassBMember_33665" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="15.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33671" xlink:to="us-gaap_PreferredStockSharesAuthorized_33677" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33671" xlink:to="us-gaap_PreferredStockParOrStatedValuePerShare_33676" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="468.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33671" xlink:to="us-gaap_CommonStockSharesOutstanding_34125" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="20.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33671" xlink:to="us-gaap_CommonStockSharesIssued_33682" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="19.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33671" xlink:to="us-gaap_CommonStockSharesAuthorized_33681" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="18.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33671" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare_33680" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="16.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33671" xlink:to="us-gaap_PreferredStockSharesIssued_33678" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="159.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementOfFinancialPositionAbstract_33660" xlink:to="us-gaap_StatementTable_33661" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="169.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementTable_33661" xlink:to="us-gaap_StatementLineItems_33671" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="160.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementTable_33661" xlink:to="us-gaap_StatementClassOfStockAxis_33662" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="17.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33671" xlink:to="us-gaap_PreferredStockSharesOutstanding_33679" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33671" xlink:to="us-gaap_TemporaryEquityRedemptionPricePerShare_33674" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33671" xlink:to="us-gaap_TemporaryEquitySharesIssued_33673" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33671" xlink:to="us-gaap_TemporaryEquitySharesOutstanding_33720" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/DescriptionofOrganizationandBusinessOperationsDetails" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis_33691" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_33701" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain" xlink:label="us-gaap_RelatedPartyDomain_33702" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_PublicSharesMember" xlink:label="onch_PublicSharesMember_33711" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_PrivatePlacementWarrantsMember" xlink:label="onch_PrivatePlacementWarrantsMember_33700" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_PercentageOfPublicSharesToBeRedeemedOnNonCompletionOfBusinessCombination" xlink:label="onch_PercentageOfPublicSharesToBeRedeemedOnNonCompletionOfBusinessCombination_33658" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceInitialPublicOffering" xlink:label="us-gaap_ProceedsFromIssuanceInitialPublicOffering_33643" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_BusinessAcquisitionPercentageOfVotingInterestsToBeAcquiredOnPostTransactionEntityMinimum" xlink:label="onch_BusinessAcquisitionPercentageOfVotingInterestsToBeAcquiredOnPostTransactionEntityMinimum_33655" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract_33618" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight_33646" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_33647" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_OtherOfferingCosts" xlink:label="onch_OtherOfferingCosts_33653" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_DeferredUnderwritingFees" xlink:label="onch_DeferredUnderwritingFees_33652" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_DescriptionOfOrganizationBusinessOperationsLiquidityAndCapitalResourcesTable" xlink:label="onch_DescriptionOfOrganizationBusinessOperationsLiquidityAndCapitalResourcesTable_33620" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_InterestToBePayDissolutionExpenses" xlink:label="onch_InterestToBePayDissolutionExpenses_33669" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_InvestmentsMaximumMaturityTerm" xlink:label="onch_InvestmentsMaximumMaturityTerm_33657" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_CashUnderwritingFees" xlink:label="onch_CashUnderwritingFees_33651" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain_33697" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_WorkingCapital" xlink:label="onch_WorkingCapital_33675" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_PercentageOfFairMarketValueEqualToNetBalanceInTrustAccount" xlink:label="onch_PercentageOfFairMarketValueEqualToNetBalanceInTrustAccount_33654" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationDateOfIncorporation" xlink:label="dei_EntityIncorporationDateOfIncorporation_33638" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfWarrants" xlink:label="us-gaap_ProceedsFromIssuanceOfWarrants_33649" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_33685" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesIssuedPricePerShare" xlink:label="us-gaap_SharesIssuedPricePerShare_33642" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues_33641" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_33684" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstandingTerm" xlink:label="us-gaap_WarrantsAndRightsOutstandingTerm_33648" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_RedeemableWarrantMember" xlink:label="onch_RedeemableWarrantMember_33698" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_SponsorMember" xlink:label="onch_SponsorMember_33703" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_TransactionCosts" xlink:label="onch_TransactionCosts_33650" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_33672" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain_33692" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis_33696" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems" xlink:label="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember" xlink:label="us-gaap_CommonClassAMember_33694" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IPOMember" xlink:label="us-gaap_IPOMember_33686" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OverAllotmentOptionMember" xlink:label="us-gaap_OverAllotmentOptionMember_33690" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOrSaleOfEquity" xlink:label="us-gaap_ProceedsFromIssuanceOrSaleOfEquity_33656" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_CantorFitzgeraldCoMember" xlink:label="onch_CantorFitzgeraldCoMember_33704" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_DescriptionOfOrganizationBusinessOperationsLiquidityAndCapitalResourcesTable_33620" xlink:to="us-gaap_StatementClassOfStockAxis_33691" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_DescriptionOfOrganizationBusinessOperationsLiquidityAndCapitalResourcesTable_33620" xlink:to="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_33701" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="200.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_33701" xlink:to="us-gaap_RelatedPartyDomain_33702" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="208.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_33692" xlink:to="onch_PublicSharesMember_33711" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="198.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfWarrantOrRightDomain_33697" xlink:to="onch_PrivatePlacementWarrantsMember_33700" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="157.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="onch_PercentageOfPublicSharesToBeRedeemedOnNonCompletionOfBusinessCombination_33658" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="142.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="us-gaap_ProceedsFromIssuanceInitialPublicOffering_33643" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="154.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="onch_BusinessAcquisitionPercentageOfVotingInterestsToBeAcquiredOnPostTransactionEntityMinimum_33655" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="145.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight_33646" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="146.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_33647" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="152.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="onch_OtherOfferingCosts_33653" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="151.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="onch_DeferredUnderwritingFees_33652" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="119.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract_33618" xlink:to="onch_DescriptionOfOrganizationBusinessOperationsLiquidityAndCapitalResourcesTable_33620" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="167.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="onch_InterestToBePayDissolutionExpenses_33669" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="156.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="onch_InvestmentsMaximumMaturityTerm_33657" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="150.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="onch_CashUnderwritingFees_33651" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="195.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfWarrantOrRightAxis_33696" xlink:to="us-gaap_ClassOfWarrantOrRightDomain_33697" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="173.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="onch_WorkingCapital_33675" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="153.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="onch_PercentageOfFairMarketValueEqualToNetBalanceInTrustAccount_33654" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="137.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="dei_EntityIncorporationDateOfIncorporation_33638" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="148.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="us-gaap_ProceedsFromIssuanceOfWarrants_33649" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="183.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SubsidiarySaleOfStockAxis_33684" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain_33685" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="141.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="us-gaap_SharesIssuedPricePerShare_33642" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="140.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues_33641" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_DescriptionOfOrganizationBusinessOperationsLiquidityAndCapitalResourcesTable_33620" xlink:to="us-gaap_SubsidiarySaleOfStockAxis_33684" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="147.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="us-gaap_WarrantsAndRightsOutstandingTerm_33648" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="196.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfWarrantOrRightDomain_33697" xlink:to="onch_RedeemableWarrantMember_33698" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="201.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyDomain_33702" xlink:to="onch_SponsorMember_33703" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="149.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="onch_TransactionCosts_33650" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="170.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_33672" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="190.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementClassOfStockAxis_33691" xlink:to="us-gaap_ClassOfStockDomain_33692" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_DescriptionOfOrganizationBusinessOperationsLiquidityAndCapitalResourcesTable_33620" xlink:to="us-gaap_ClassOfWarrantOrRightAxis_33696" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="15.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_DescriptionOfOrganizationBusinessOperationsLiquidityAndCapitalResourcesTable_33620" xlink:to="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="192.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_33692" xlink:to="us-gaap_CommonClassAMember_33694" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="184.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain_33685" xlink:to="us-gaap_IPOMember_33686" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="188.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain_33685" xlink:to="us-gaap_OverAllotmentOptionMember_33690" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="155.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems_33627" xlink:to="us-gaap_ProceedsFromIssuanceOrSaleOfEquity_33656" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="202.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyDomain_33702" xlink:to="onch_CantorFitzgeraldCoMember_33704" preferredLabel="http://www.xbrl.org/2003/role/label" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/DescriptionofOrganizationandBusinessOperations" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock_33616" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract_33615" />
    <link:presentationArc xlink:type="arc" order="116.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract_33615" xlink:to="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock_33616" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/CondensedStatementsofChangesinShareholdersDeficitUnaudited" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity_33626" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis_1070" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember" xlink:label="us-gaap_RetainedEarningsMember_1069" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember" xlink:label="us-gaap_CommonClassAMember_1072" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain_1074" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems_1075" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis_1066" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesOutstanding" xlink:label="us-gaap_SharesOutstanding_33602" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesOutstanding" xlink:label="us-gaap_SharesOutstanding_33621" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable_1065" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfStockholdersEquityAbstract" xlink:label="us-gaap_StatementOfStockholdersEquityAbstract_1064" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity_33581" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityAccretionToRedemptionValue" xlink:label="us-gaap_TemporaryEquityAccretionToRedemptionValue_33598" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="us-gaap_AdditionalPaidInCapitalMember_1068" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassBMember" xlink:label="us-gaap_CommonClassBMember_1073" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember_1067" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain_1071" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss_33582" />
    <link:presentationArc xlink:type="arc" order="20.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_1075" xlink:to="us-gaap_StockholdersEquity_33626" preferredLabel="http://www.xbrl.org/2003/role/periodEndLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementTable_1065" xlink:to="us-gaap_StatementClassOfStockAxis_1070" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="74.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementEquityComponentsAxis_1066" xlink:to="us-gaap_RetainedEarningsMember_1069" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="77.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementClassOfStockAxis_1070" xlink:to="us-gaap_CommonClassAMember_1072" preferredLabel="http://www.xbrl.org/2009/role/netLabel" />
    <link:presentationArc xlink:type="arc" order="79.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementClassOfStockAxis_1070" xlink:to="us-gaap_ClassOfStockDomain_1074" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementTable_1065" xlink:to="us-gaap_StatementLineItems_1075" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementTable_1065" xlink:to="us-gaap_StatementEquityComponentsAxis_1066" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_1075" xlink:to="us-gaap_SharesOutstanding_33602" preferredLabel="http://www.xbrl.org/2003/role/periodStartLabel" />
    <link:presentationArc xlink:type="arc" order="21.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_1075" xlink:to="us-gaap_SharesOutstanding_33621" preferredLabel="http://www.xbrl.org/2003/role/periodEndLabel" />
    <link:presentationArc xlink:type="arc" order="70.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementOfStockholdersEquityAbstract_1064" xlink:to="us-gaap_StatementTable_1065" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_1075" xlink:to="us-gaap_StockholdersEquity_33581" preferredLabel="http://www.xbrl.org/2003/role/periodStartLabel" />
    <link:presentationArc xlink:type="arc" order="18.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_1075" xlink:to="us-gaap_TemporaryEquityAccretionToRedemptionValue_33598" preferredLabel="http://www.xbrl.org/2009/role/negatedLabel" />
    <link:presentationArc xlink:type="arc" order="73.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementEquityComponentsAxis_1066" xlink:to="us-gaap_AdditionalPaidInCapitalMember_1068" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="78.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementClassOfStockAxis_1070" xlink:to="us-gaap_CommonClassBMember_1073" preferredLabel="http://www.xbrl.org/2009/role/netLabel" />
    <link:presentationArc xlink:type="arc" order="72.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementEquityComponentsAxis_1066" xlink:to="us-gaap_CommonStockMember_1067" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="76.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementEquityComponentsAxis_1066" xlink:to="us-gaap_EquityComponentDomain_1071" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="19.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_1075" xlink:to="us-gaap_NetIncomeLoss_33582" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/InitialPublicOfferingDetails" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockPricePerShare" xlink:label="us-gaap_SaleOfStockPricePerShare_33787" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable" xlink:label="us-gaap_ScheduleOfStockByClassTable_33723" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight_33774" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_33775" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_NumberOfSharesIssuedPerUnit" xlink:label="onch_NumberOfSharesIssuedPerUnit_33773" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember" xlink:label="us-gaap_CommonClassAMember_33733" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IPOMember" xlink:label="us-gaap_IPOMember_33736" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OverAllotmentOptionMember" xlink:label="us-gaap_OverAllotmentOptionMember_33737" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_33735" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockLineItems" xlink:label="us-gaap_SubsidiarySaleOfStockLineItems_34131" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_33734" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis_33731" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstandingTerm" xlink:label="us-gaap_WarrantsAndRightsOutstandingTerm_33776" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_NumberOfWarrantsIssuedPerUnit" xlink:label="onch_NumberOfWarrantsIssuedPerUnit_33790" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_PublicWarrantsMember" xlink:label="onch_PublicWarrantsMember_33730" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_RedeemableWarrantMember" xlink:label="onch_RedeemableWarrantMember_33729" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesIssuedPricePerShare" xlink:label="us-gaap_SharesIssuedPricePerShare_33769" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantMember" xlink:label="us-gaap_WarrantMember_33728" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain_33726" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis_33724" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDisclosuresAbstract" xlink:label="us-gaap_ClassOfStockDisclosuresAbstract_33722" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_UnitsIssuedDuringPeriodSharesNewIssues" xlink:label="onch_UnitsIssuedDuringPeriodSharesNewIssues_33739" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain_33732" />
    <link:presentationArc xlink:type="arc" order="21.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems_34131" xlink:to="us-gaap_SaleOfStockPricePerShare_33787" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="218.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDisclosuresAbstract_33722" xlink:to="us-gaap_ScheduleOfStockByClassTable_33723" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems_34131" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight_33774" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="15.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems_34131" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_33775" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems_34131" xlink:to="onch_NumberOfSharesIssuedPerUnit_33773" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="228.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_33732" xlink:to="us-gaap_CommonClassAMember_33733" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="231.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain_33735" xlink:to="us-gaap_IPOMember_33736" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="232.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain_33735" xlink:to="us-gaap_OverAllotmentOptionMember_33737" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="230.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SubsidiarySaleOfStockAxis_33734" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain_33735" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="474.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ScheduleOfStockByClassTable_33723" xlink:to="us-gaap_SubsidiarySaleOfStockLineItems_34131" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="229.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ScheduleOfStockByClassTable_33723" xlink:to="us-gaap_SubsidiarySaleOfStockAxis_33734" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="226.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ScheduleOfStockByClassTable_33723" xlink:to="us-gaap_StatementClassOfStockAxis_33731" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="16.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems_34131" xlink:to="us-gaap_WarrantsAndRightsOutstandingTerm_33776" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems_34131" xlink:to="onch_NumberOfWarrantsIssuedPerUnit_33790" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="225.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfWarrantOrRightDomain_33726" xlink:to="onch_PublicWarrantsMember_33730" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="224.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfWarrantOrRightDomain_33726" xlink:to="onch_RedeemableWarrantMember_33729" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems_34131" xlink:to="us-gaap_SharesIssuedPricePerShare_33769" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="223.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfWarrantOrRightDomain_33726" xlink:to="us-gaap_WarrantMember_33728" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="221.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfWarrantOrRightAxis_33724" xlink:to="us-gaap_ClassOfWarrantOrRightDomain_33726" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="219.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ScheduleOfStockByClassTable_33723" xlink:to="us-gaap_ClassOfWarrantOrRightAxis_33724" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems_34131" xlink:to="onch_UnitsIssuedDuringPeriodSharesNewIssues_33739" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="227.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementClassOfStockAxis_33731" xlink:to="us-gaap_ClassOfStockDomain_33732" preferredLabel="http://www.xbrl.org/2003/role/label" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/FairValueMeasurementsScheduleofCompanysAssetsThatareMeasuredatFairValueonaRecurringBasisDetails" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis_34049" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_34052" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_USTreasurySecuritiesMember" xlink:label="us-gaap_USTreasurySecuritiesMember_34056" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsFairValueDisclosureAbstract" xlink:label="us-gaap_AssetsFairValueDisclosureAbstract_34057" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsHeldInTrustNoncurrent" xlink:label="us-gaap_AssetsHeldInTrustNoncurrent_34053" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAxis" xlink:label="us-gaap_CashAndCashEquivalentsAxis_34054" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract_34044" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_34045" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_34182" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_34055" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_34050" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member_34051" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_34045" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis_34049" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_34045" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_34052" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="417.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_34055" xlink:to="us-gaap_USTreasurySecuritiesMember_34056" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="418.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_34052" xlink:to="us-gaap_AssetsFairValueDisclosureAbstract_34057" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AssetsFairValueDisclosureAbstract_34057" xlink:to="us-gaap_AssetsHeldInTrustNoncurrent_34053" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_34045" xlink:to="us-gaap_CashAndCashEquivalentsAxis_34054" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="406.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract_34044" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_34045" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AssetsFairValueDisclosureAbstract_34057" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_34182" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="416.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CashAndCashEquivalentsAxis_34054" xlink:to="us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_34055" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="411.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis_34049" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_34050" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="412.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_34050" xlink:to="us-gaap_FairValueInputsLevel1Member_34051" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/CondensedStatementsofCashFlowsUnaudited" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InvestmentIncomeInterest" xlink:label="us-gaap_InvestmentIncomeInterest_33782" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInPrepaidInsurance" xlink:label="us-gaap_IncreaseDecreaseInPrepaidInsurance_33786" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_33771" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_PaymentOfOperationCostsThroughPromissoryNoteRelatedParty" xlink:label="onch_PaymentOfOperationCostsThroughPromissoryNoteRelatedParty_33778" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_33801" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_DeferredOfferingCostsPaidThroughPromissoryNoteRelatedParty" xlink:label="onch_DeferredOfferingCostsPaidThroughPromissoryNoteRelatedParty_34172" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_DeferredOfferingCostsAppliedToPrepaidServicesContributedBySponsor" xlink:label="onch_DeferredOfferingCostsAppliedToPrepaidServicesContributedBySponsor_34173" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_33789" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities" xlink:label="us-gaap_IncreaseDecreaseInAccruedLiabilities_33785" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_33808" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_33807" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems_33767" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementOfCashFlowsAbstract" xlink:label="us-gaap_StatementOfCashFlowsAbstract_33765" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable_33766" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect_33803" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents" xlink:label="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_33806" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_IncreaseDecreaseInLongTermPrepaidInsurance" xlink:label="onch_IncreaseDecreaseInLongTermPrepaidInsurance_34156" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_DeferredCostsIncludedInAccruedOfferingCosts" xlink:label="onch_DeferredCostsIncludedInAccruedOfferingCosts_34155" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_33800" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfStockIssuanceCosts" xlink:label="us-gaap_PaymentsOfStockIssuanceCosts_33799" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss_33772" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_33770" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_33788" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_33771" xlink:to="us-gaap_InvestmentIncomeInterest_33782" preferredLabel="http://www.xbrl.org/2009/role/negatedLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_33789" xlink:to="us-gaap_IncreaseDecreaseInPrepaidInsurance_33786" preferredLabel="http://www.xbrl.org/2009/role/negatedLabel" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_33770" xlink:to="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_33771" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_33771" xlink:to="onch_PaymentOfOperationCostsThroughPromissoryNoteRelatedParty_33778" preferredLabel="http://www.xbrl.org/2009/role/negatedLabel" />
    <link:presentationArc xlink:type="arc" order="274.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33767" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_33801" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="498.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_33808" xlink:to="onch_DeferredOfferingCostsPaidThroughPromissoryNoteRelatedParty_34172" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="499.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_33808" xlink:to="onch_DeferredOfferingCostsAppliedToPrepaidServicesContributedBySponsor_34173" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_33770" xlink:to="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_33789" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_33789" xlink:to="us-gaap_IncreaseDecreaseInAccruedLiabilities_33785" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="279.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33767" xlink:to="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_33808" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="278.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33767" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_33807" preferredLabel="http://www.xbrl.org/2003/role/periodEndLabel" />
    <link:presentationArc xlink:type="arc" order="241.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementTable_33766" xlink:to="us-gaap_StatementLineItems_33767" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="240.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementOfCashFlowsAbstract_33765" xlink:to="us-gaap_StatementTable_33766" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="276.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33767" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseExcludingExchangeRateEffect_33803" preferredLabel="http://www.xbrl.org/2003/role/totalLabel" />
    <link:presentationArc xlink:type="arc" order="277.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33767" xlink:to="us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_33806" preferredLabel="http://www.xbrl.org/2003/role/periodStartLabel" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_33789" xlink:to="onch_IncreaseDecreaseInLongTermPrepaidInsurance_34156" preferredLabel="http://www.xbrl.org/2009/role/negatedLabel" />
    <link:presentationArc xlink:type="arc" order="488.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_33808" xlink:to="onch_DeferredCostsIncludedInAccruedOfferingCosts_34155" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="15.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_33801" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities_33800" preferredLabel="http://www.xbrl.org/2003/role/totalLabel" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_33801" xlink:to="us-gaap_PaymentsOfStockIssuanceCosts_33799" preferredLabel="http://www.xbrl.org/2009/role/negatedLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_33770" xlink:to="us-gaap_NetIncomeLoss_33772" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="244.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementLineItems_33767" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_33770" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_33770" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities_33788" preferredLabel="http://www.xbrl.org/2003/role/totalLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/FairValueMeasurementsDetails" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantsAndRightsOutstanding" xlink:label="us-gaap_WarrantsAndRightsOutstanding_34169" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_34168" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_34077" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_34076" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_PublicWarrantsMember" xlink:label="onch_PublicWarrantsMember_34075" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis_34073" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain_34074" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_34070" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_34060" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract_34059" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IPOMember" xlink:label="us-gaap_IPOMember_34078" />
    <link:presentationArc xlink:type="arc" order="496.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_34070" xlink:to="us-gaap_WarrantsAndRightsOutstanding_34169" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="495.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_34070" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_34168" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="433.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SubsidiarySaleOfStockAxis_34076" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain_34077" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="15.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_34060" xlink:to="us-gaap_SubsidiarySaleOfStockAxis_34076" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfWarrantOrRightDomain_34074" xlink:to="onch_PublicWarrantsMember_34075" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_34060" xlink:to="us-gaap_ClassOfWarrantOrRightAxis_34073" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="431.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfWarrantOrRightAxis_34073" xlink:to="us-gaap_ClassOfWarrantOrRightDomain_34074" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="16.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_34060" xlink:to="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_34070" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisAbstract_34059" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_34060" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="434.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain_34077" xlink:to="us-gaap_IPOMember_34078" preferredLabel="http://www.xbrl.org/2003/role/label" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/SegmentInformationDetails" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingCodmProfitLossMeasureHowUsedDescription" xlink:label="us-gaap_SegmentReportingCodmProfitLossMeasureHowUsedDescription_34089" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NumberOfReportableSegments" xlink:label="us-gaap_NumberOfReportableSegments_34088" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingCodmIndividualTitleAndPositionOrGroupOrCommitteeNameExtensibleEnumeration" xlink:label="us-gaap_SegmentReportingCodmIndividualTitleAndPositionOrGroupOrCommitteeNameExtensibleEnumeration_34090" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingAbstract" xlink:label="us-gaap_SegmentReportingAbstract_34087" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SegmentReportingAbstract_34087" xlink:to="us-gaap_SegmentReportingCodmProfitLossMeasureHowUsedDescription_34089" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SegmentReportingAbstract_34087" xlink:to="us-gaap_NumberOfReportableSegments_34088" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SegmentReportingAbstract_34087" xlink:to="us-gaap_SegmentReportingCodmIndividualTitleAndPositionOrGroupOrCommitteeNameExtensibleEnumeration_34090" preferredLabel="http://www.xbrl.org/2003/role/label" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/SegmentInformationScheduleofPerformanceandMakingKeyDecisionsRegardingResourceAllocationDetails" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsHeldInTrustNoncurrent" xlink:label="us-gaap_AssetsHeldInTrustNoncurrent_34094" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GeneralAndAdministrativeExpense" xlink:label="us-gaap_GeneralAndAdministrativeExpense_34095" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_34093" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingAbstract" xlink:label="us-gaap_SegmentReportingAbstract_34092" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SegmentReportingAbstract_34092" xlink:to="us-gaap_AssetsHeldInTrustNoncurrent_34094" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SegmentReportingAbstract_34092" xlink:to="us-gaap_GeneralAndAdministrativeExpense_34095" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SegmentReportingAbstract_34092" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_34093" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/SubsequentEvents" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventsAbstract" xlink:label="us-gaap_SubsequentEventsAbstract_34098" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsequentEventsTextBlock" xlink:label="us-gaap_SubsequentEventsTextBlock_34099" />
    <link:presentationArc xlink:type="arc" order="447.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SubsequentEventsAbstract_34098" xlink:to="us-gaap_SubsequentEventsTextBlock_34099" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/PrivatePlacementDetails" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain_33756" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_CantorFitzgeraldCoMember" xlink:label="onch_CantorFitzgeraldCoMember_33764" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_PercentageOfPublicSharesToBeRedeemedOnNonCompletionOfBusinessCombination" xlink:label="onch_PercentageOfPublicSharesToBeRedeemedOnNonCompletionOfBusinessCombination_33751" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_PrivatePlacementAbstract" xlink:label="onch_PrivatePlacementAbstract_33745" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_PrivatePlacementTable" xlink:label="onch_PrivatePlacementTable_33746" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis_33752" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="us-gaap_StatementClassOfStockAxis_33755" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain_33753" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_PrivatePlacementWarrantsMember" xlink:label="onch_PrivatePlacementWarrantsMember_33760" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrivatePlacementMember" xlink:label="us-gaap_PrivatePlacementMember_33754" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain" xlink:label="us-gaap_RelatedPartyDomain_33762" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_33761" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfWarrants" xlink:label="us-gaap_ProceedsFromIssuanceOfWarrants_33750" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember" xlink:label="us-gaap_CommonClassAMember_33757" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight_33748" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_33749" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain_33759" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis_33758" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockLineItems" xlink:label="us-gaap_ClassOfStockLineItems_33747" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_SponsorMember" xlink:label="onch_SponsorMember_33763" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_StatementClassOfStockAxis_33755" xlink:to="us-gaap_ClassOfStockDomain_33756" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyDomain_33762" xlink:to="onch_CantorFitzgeraldCoMember_33764" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33747" xlink:to="onch_PercentageOfPublicSharesToBeRedeemedOnNonCompletionOfBusinessCombination_33751" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="238.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_PrivatePlacementAbstract_33745" xlink:to="onch_PrivatePlacementTable_33746" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_PrivatePlacementTable_33746" xlink:to="us-gaap_SubsidiarySaleOfStockAxis_33752" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_PrivatePlacementTable_33746" xlink:to="us-gaap_StatementClassOfStockAxis_33755" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SubsidiarySaleOfStockAxis_33752" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain_33753" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfWarrantOrRightDomain_33759" xlink:to="onch_PrivatePlacementWarrantsMember_33760" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain_33753" xlink:to="us-gaap_PrivatePlacementMember_33754" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_33761" xlink:to="us-gaap_RelatedPartyDomain_33762" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_PrivatePlacementTable_33746" xlink:to="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_33761" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33747" xlink:to="us-gaap_ProceedsFromIssuanceOfWarrants_33750" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDomain_33756" xlink:to="us-gaap_CommonClassAMember_33757" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33747" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight_33748" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockLineItems_33747" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_33749" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfWarrantOrRightAxis_33758" xlink:to="us-gaap_ClassOfWarrantOrRightDomain_33759" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_PrivatePlacementTable_33746" xlink:to="us-gaap_ClassOfWarrantOrRightAxis_33758" preferredLabel="http://www.xbrl.org/2003/role/label" />
    <link:presentationArc xlink:type="arc" order="15.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="onch_PrivatePlacementTable_33746" xlink:to="us-gaap_ClassOfStockLineItems_33747" preferredLabel="http://www.xbrl.org/2003/role/verboseLabel" />
    <link:presentationArc xlink:type="arc" order="10.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_RelatedPartyDomain_33762" xlink:to="onch_SponsorMember_33763" preferredLabel="http://www.xbrl.org/2003/role/label" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/SummaryofSignificantAccountingPoliciesPolicies" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxPolicyTextBlock" xlink:label="us-gaap_IncomeTaxPolicyTextBlock_33843" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesSubjectToMandatoryRedemptionChangesInRedemptionValuePolicyTextBlock" xlink:label="us-gaap_SharesSubjectToMandatoryRedemptionChangesInRedemptionValuePolicyTextBlock_33844" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskCreditRisk" xlink:label="us-gaap_ConcentrationRiskCreditRisk_33839" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativesPolicyTextBlock" xlink:label="us-gaap_DerivativesPolicyTextBlock_33845" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerSharePolicyTextBlock" xlink:label="us-gaap_EarningsPerSharePolicyTextBlock_33846" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueOfFinancialInstrumentsPolicy" xlink:label="us-gaap_FairValueOfFinancialInstrumentsPolicy_33841" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MarketableSecuritiesPolicy" xlink:label="us-gaap_MarketableSecuritiesPolicy_33838" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_33847" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_UseOfEstimates" xlink:label="us-gaap_UseOfEstimates_33836" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsPolicyTextBlock" xlink:label="us-gaap_CashAndCashEquivalentsPolicyTextBlock_33837" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_EmergingGrowthCompanyPolicyTextBlock" xlink:label="onch_EmergingGrowthCompanyPolicyTextBlock_33835" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountingPoliciesAbstract" xlink:label="us-gaap_AccountingPoliciesAbstract_33833" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_33834" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_OfferingCostsPolicyTextBlock" xlink:label="onch_OfferingCostsPolicyTextBlock_33840" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_WarrantInstrumentsPolicyTextBlock" xlink:label="onch_WarrantInstrumentsPolicyTextBlock_33848" />
    <link:presentationArc xlink:type="arc" order="20.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33833" xlink:to="us-gaap_IncomeTaxPolicyTextBlock_33843" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="19.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33833" xlink:to="us-gaap_SharesSubjectToMandatoryRedemptionChangesInRedemptionValuePolicyTextBlock_33844" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="16.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33833" xlink:to="us-gaap_ConcentrationRiskCreditRisk_33839" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="21.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33833" xlink:to="us-gaap_DerivativesPolicyTextBlock_33845" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="23.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33833" xlink:to="us-gaap_EarningsPerSharePolicyTextBlock_33846" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="18.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33833" xlink:to="us-gaap_FairValueOfFinancialInstrumentsPolicy_33841" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="15.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33833" xlink:to="us-gaap_MarketableSecuritiesPolicy_33838" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="24.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33833" xlink:to="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_33847" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="13.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33833" xlink:to="us-gaap_UseOfEstimates_33836" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="14.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33833" xlink:to="us-gaap_CashAndCashEquivalentsPolicyTextBlock_33837" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="12.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33833" xlink:to="onch_EmergingGrowthCompanyPolicyTextBlock_33835" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="11.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33833" xlink:to="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_33834" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="17.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33833" xlink:to="onch_OfferingCostsPolicyTextBlock_33840" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="22.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33833" xlink:to="onch_WarrantInstrumentsPolicyTextBlock_33848" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/SummaryofSignificantAccountingPoliciesTables" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock" xlink:label="us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock_33852" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountingPoliciesAbstract" xlink:label="us-gaap_AccountingPoliciesAbstract_33850" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TemporaryEquityTableTextBlock" xlink:label="us-gaap_TemporaryEquityTableTextBlock_33851" />
    <link:presentationArc xlink:type="arc" order="294.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33850" xlink:to="us-gaap_ScheduleOfEarningsPerShareBasicAndDilutedTableTextBlock_33852" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="293.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33850" xlink:to="us-gaap_TemporaryEquityTableTextBlock_33851" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/SummaryofSignificantAccountingPolicies" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountingPoliciesAbstract" xlink:label="us-gaap_AccountingPoliciesAbstract_33830" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SignificantAccountingPoliciesTextBlock" xlink:label="us-gaap_SignificantAccountingPoliciesTextBlock_33831" />
    <link:presentationArc xlink:type="arc" order="290.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_AccountingPoliciesAbstract_33830" xlink:to="us-gaap_SignificantAccountingPoliciesTextBlock_33831" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/FairValueMeasurements" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosuresTextBlock" xlink:label="us-gaap_FairValueDisclosuresTextBlock_34025" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosuresAbstract" xlink:label="us-gaap_FairValueDisclosuresAbstract_34024" />
    <link:presentationArc xlink:type="arc" order="395.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_FairValueDisclosuresAbstract_34024" xlink:to="us-gaap_FairValueDisclosuresTextBlock_34025" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/FairValueMeasurementsTables" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTableTextBlock" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTableTextBlock_34030" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueDisclosuresAbstract" xlink:label="us-gaap_FairValueDisclosuresAbstract_34029" />
    <link:presentationArc xlink:type="arc" order="398.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_FairValueDisclosuresAbstract_34029" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTableTextBlock_34030" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/SegmentInformationTables" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingAbstract" xlink:label="us-gaap_SegmentReportingAbstract_34084" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTextBlock" xlink:label="us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTextBlock_34085" />
    <link:presentationArc xlink:type="arc" order="438.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SegmentReportingAbstract_34084" xlink:to="us-gaap_ReconciliationOfOperatingProfitLossFromSegmentsToConsolidatedTextBlock_34085" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/CommitmentsandContingency" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_33941" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingenciesDisclosureAbstract" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureAbstract_33940" />
    <link:presentationArc xlink:type="arc" order="364.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_CommitmentsAndContingenciesDisclosureAbstract_33940" xlink:to="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_33941" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/PrivatePlacement" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_PrivatePlacementTextBlock" xlink:label="onch_PrivatePlacementTextBlock_33743" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDisclosuresAbstract" xlink:label="us-gaap_ClassOfStockDisclosuresAbstract_33742" />
    <link:presentationArc xlink:type="arc" order="236.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDisclosuresAbstract_33742" xlink:to="onch_PrivatePlacementTextBlock_33743" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/InitialPublicOffering" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDisclosuresAbstract" xlink:label="us-gaap_ClassOfStockDisclosuresAbstract_33709" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_InitialPublicOfferingDisclosureTextBlock" xlink:label="onch_InitialPublicOfferingDisclosureTextBlock_33710" />
    <link:presentationArc xlink:type="arc" order="207.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_ClassOfStockDisclosuresAbstract_33709" xlink:to="onch_InitialPublicOfferingDisclosureTextBlock_33710" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://onch.com/20260630/role/SegmentInformation" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingAbstract" xlink:label="us-gaap_SegmentReportingAbstract_34081" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SegmentReportingDisclosureTextBlock" xlink:label="us-gaap_SegmentReportingDisclosureTextBlock_34082" />
    <link:presentationArc xlink:type="arc" order="436.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="us-gaap_SegmentReportingAbstract_34081" xlink:to="us-gaap_SegmentReportingDisclosureTextBlock_34082" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
  <link:presentationLink xlink:role="http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements" xlink:title="presentationLink" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_Rule10b51ArrangementModifiedFlag" xlink:label="onch_Rule10b51ArrangementModifiedFlag_34174" />
    <link:loc xlink:type="locator" xlink:href="onch-20260630.xsd#onch_NonRule10b51ArrangementModifiedFlag" xlink:label="onch_NonRule10b51ArrangementModifiedFlag_34175" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/ecd/2026/ecd-2026.xsd#ecd_InsiderTradingArrLineItems" xlink:label="ecd_InsiderTradingArrLineItems_34105" />
    <link:presentationArc xlink:type="arc" order="500.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="ecd_InsiderTradingArrLineItems_34105" xlink:to="onch_Rule10b51ArrangementModifiedFlag_34174" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
    <link:presentationArc xlink:type="arc" order="501.00000" priority="1" use="optional" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="ecd_InsiderTradingArrLineItems_34105" xlink:to="onch_NonRule10b51ArrangementModifiedFlag_34175" preferredLabel="http://www.xbrl.org/2003/role/terseLabel" />
  </link:presentationLink>
</link:linkbase>
