Exhibit 99.4

Execution Version

COINCHECK GROUP N.V.

ACKNOWLEDGEMENT AGREEMENT

May 12, 2026

TABLE OF CONTENTS

ACKNOWLEDGEMENT AGREEMENT

THIS ACKNOWLEDGEMENT AGREEMENT (THIS “AGREEMENT”) IS DATED MAY 12, 2026 (THE “EXECUTION DATE”) AND MADE BETWEEN:

together the “Parties” and each a “Party.”

BACKGROUND:

WHEREAS, KDDI and Coincheck Group N.V. (the “Company”) have entered into the “Share Subscription and Investor Rights Agreement” dated as of the Execution Date (the “SSA”);

WHEREAS, pursuant to the SSA, KDDI has the right, in accordance with the terms of the SSA, to designate one (1) non-executive director nominee to serve on the board of directors of the Company; and

WHEREAS, Monex has agreed to enter into this Agreement with KDDI to confirm its acknowledgement of the said right of KDDI, and the execution and delivery of this Agreement by the Parties is a condition precedent to the completion and closing of the SSA.

NOW, THEREFORE, in consideration of the mutual covenants and agreements hereinafter set forth and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the Parties agree as follows:

The terms set out in Exhibit 1.1, when used in this Agreement, shall have the meanings ascribed to them therein.

Except for the provisions of Sections 1, 3, and 4, which shall take effect on the Execution Date, this Agreement shall enter into effect on the date KDDI becomes a holder of the Company’s ordinary shares (“Ordinary Shares”) issued by the Company pursuant to the SSA.

The obligations and claims of each Party under this Agreement to the other Party shall not constitute joint and several liabilities with any other Person.

The Parties acknowledge and agree that this Agreement is solely about Monex agreeing to vote its Ordinary Shares in a manner consistent with KDDI’s rights to nominate the Investor Nominee under the SSA, and that this Agreement contemplates no information sharing by Monex regarding Company business, affairs, or other information, and that any information rights KDDI may have concerning the Company are set forth in, and governed by, solely the SSA and applicable Law.

No amendment of this Agreement shall be effective unless such amendment is in writing and signed by or on behalf of each Party.

Except as otherwise agreed by the Parties, no Party may assign this Agreement or assign or encumber any of their rights under this Agreement to any other Person, without the written consent of the other Party; it being understood that without this consent, no assignment, encumbrance or transfer may be effected.

If any provision of this Agreement becomes or is declared by a court of competent jurisdiction to be illegal, unenforceable or void, such provision or part shall to that extent be deemed not to form part of this Agreement, but the legality, validity and enforceability of the remainder of this Agreement shall not be affected. The Parties shall use reasonable efforts to agree a replacement provision that is legal, valid and enforceable and that achieves, so far as possible, the intended effect of the illegal, invalid or unenforceable provision.

No failure to exercise, nor any delay in exercising, by a Party, any right or remedy under this Agreement will operate as a waiver. No single or partial exercise of any right or remedy will prevent any further or other exercise or the exercise of any other right or remedy.

The Parties shall consult with each other before issuing press releases or otherwise making any public statements with respect to this Agreement, and neither Party shall issue any such press release or public statement without the prior written consent of the other Party, provided that such consent shall not be required to the extent the public announcement is (i) required by Law or by the rules, requests, orders, notices, administrative guidance, or other determinations, whether oral or in writing, of any Governmental Authority, and (ii) following reasonable consultation with the other Party, cannot or can no longer be delayed under applicable Law.

Each Party shall bear and pay all of its own expenses in connection with this Agreement and the transactions contemplated hereby.

This Agreement shall be governed by, and construed in accordance with, the laws of Japan. With respect to any dispute arising out of or in relation to this Agreement, the Parties shall first discuss with each other in good faith with a view to resolving such dispute. If the Parties are not able to reach an agreement through such discussion, the Parties agree to submit to the exclusive jurisdiction of the Tokyo District Court to resolve such dispute.

This Agreement may be entered into in any number of counterparts, all of which taken together shall constitute one and the same instrument. The Parties may enter into this Agreement by signing any such counterpart.

This Agreement contains the entire agreement between the Parties relating to the subject matter of this Agreement, to the exclusion of any terms implied by Law which may be excluded by contract, and supersedes any previous written or oral agreement between the Parties to this Agreement in relation to the matters dealt with in this Agreement.

The Parties shall at their own costs and expenses from time to time execute and procure to be executed such documents and perform and procure to be performed such acts as may be reasonable required by each of them to give the Parties the full benefit of this Agreement.

The Parties shall consult in good faith to resolve matters not set forth in this Agreement or any questions arising in connection with this Agreement.

The Parties agree that the obligations imposed on them in this Agreement are special, unique and of an extraordinary character, and that, in the event of breach by any Party, damages would not be an adequate remedy and the other Party shall be entitled to specific performance and injunctive relief in addition to any other remedy to which it may be entitled, at law or in equity; and the Parties further agree to waive any requirement for the securing or posting of any bond in connection with the obtaining of any such injunctive or other equitable relief.

(signature page follows)

IN WITNESS WHEREOF, this Agreement has been executed by the Parties as of the Execution Date.

Signature page to Acknowledgement Agreement

IN WITNESS WHEREOF, this Agreement has been executed by the Parties as of the Execution Date.

Signature page to Acknowledgement Agreement

EXHIBIT 1.1

Definitions

EXHIBIT 4.5.3

Notices

[Omitted]