X0202 SCHEDULE 13D/A 0001346609 XXXXXXXX LIVE 1 Ordinary Shares 05/12/2026 false 0001913847 N20967118 Coincheck Group N.V.

Nieuwezijds Voorburgwal 162 Amsterdam P7 1012 SJ

Yuko Seimei 81-3-4323-8698 Monex Group, Inc. ARK Mori Building 25F 1-12-32 Akasaka, Minato-ku, Tokyo M0 107-6025 0001346609 N MONEX GROUP, INC. OO N M0 136247594.00 0.00 136247594.00 0.00 136247594.00 N 83.6 CO Ordinary Shares Coincheck Group N.V. Nieuwezijds Voorburgwal 162 Amsterdam P7 1012 SJ This Amendment No. 1 ("Amendment No. 1") to Schedule 13D relates to the ordinary shares ("Ordinary Shares") of Coincheck Group N.V. (the "Issuer"), and amends and supplements the initial statement on Schedule 13D filed on March 19, 2026 (as so amended, the "Schedule 13D"). Capitalized terms used but not defined in this Amendment No. 1 shall have the same meanings ascribed to them in the Schedule 13D. Item 4 of the Schedule 13D is hereby amended and supplemented by the following: The information in Item 6 of this Schedule 13D is incorporated herein by reference. Item 6 of the Schedule 13D is hereby amended and supplemented by the following: On May 12, 2026, the Issuer and KDDI Corporation ("KDDI") entered into a Share Subscription and Investor Rights Agreement ("SSA"), pursuant to which, among other things, KDDI has the right pursuant to the SSA to designate one non-executive director nominee (the "KDDI Nominee") to serve on the board of directors of the Issuer (the "Board"). Concurrently with entering into the SSA, the Reporting Person agreed to enter into an Acknowledgement Agreement with KDDI (the "Acknowledgement Agreement"), the execution and delivery of which is a condition precedent to the completion and closing of the SSA. Pursuant to the terms of the Acknowledgement Agreement, the Reporting Person has agreed to vote all Ordinary Shares (and any other voting securities) of the Issuer held by it to elect, at each general meeting of the Issuer where the KDDI Nominee is to be voted upon, the KDDI Nominee, as proposed by the Board in accordance with the SSA and the governance documents of the Issuer, as a member of the Board, unless the appointment of such nominee would constitute a violation of any applicable laws. The Acknowledgement Agreement shall be terminated if the parties agree in writing to terminate such agreement, KDDI ceases to have the right to nominate a KDDI Nominee under the SSA, or the SSA is terminated. The foregoing description of the Acknowledgement Agreement does not purport to be complete and is qualified in its entirety by reference to the full text of such agreement, a copy of which is filed as Exhibit 99.4 to this Schedule 13D and is incorporated herein by reference. 99.4 Acknowledgement Agreement, dated as of May 12, 2026, by and between Monex Group, Inc. and KDDI Corporation MONEX GROUP, INC. /s/ Yuko Seimei 05/14/2026