UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, DC 20549 FORM 6-K REPORT OF FOREIGN PRIVATE ISSUER PURSUANT TO RULE 13a-16 OR 15d-16 UNDER THE SECURITIES EXCHANGE ACT OF 1934 For the month of October 2025 Commission File Number: 001-42438 COINCHECK GROUP N.V. (Translation of registrant’s name into English) Nieuwezijds Voorburgwal 162 1012 SJ Amsterdam The Netherlands (Address of principal executive offices) Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F: Form 20-F ☒ Form 40-F ☐ Coincheck Group N.V. (“Coincheck Group”) is providing the below update for Coincheck, Inc. (“Coincheck”). This information will also be posted at https://coincheck.com. Coincheck Group (“CNCK” and “CNCKW”) is a public limited liability company and the holding company for Coincheck. Coincheck operates one of the largest multi-cryptocurrency marketplaces and crypto asset exchanges in Japan and is regulated by the Japan Financial Services Agency. Coincheck provides Marketplace and Exchange platforms on which diverse cryptocurrencies, including Bitcoin and Ethereum, are held and exchanged as well as other retail-focused crypto services. Coincheck Group uses its website (https://www.coincheckgroup.com/) to distribute company information and makes available free of charge a variety of information for investors, including its filings with the Securities and Exchange Commission (“SEC”), as soon as reasonably practicable after electronically filing that material with, or furnishing it to, the SEC. The information that Coincheck Group posts on its website may be deemed material. Accordingly, investors should monitor Coincheck Group’s website, in addition to following its press releases, filings with the SEC, and public conference calls and webcasts. In addition, investors may opt in to automatically receive email alerts and other information about Coincheck Group when enrolling their email address by visiting the “Email Alerts” section of the Coincheck Group website. Coincheck Group does not incorporate the information contained on, or accessible through, Coincheck Group’s website, Coincheck’s website or related social media channels into this Report on Form 6-K.

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Monthly Disclosure Coincheck, Inc. is reporting the following preliminary monthly disclosure information for the past twelve months. The preliminary numbers in the tables below are based on currently available information. These preliminary estimates have not been audited by any independent registered public accountants, are subject to update and should not be extrapolated for future periods. Oct. 2024 Nov. 2024 Dec. 2024 Jan. 2025 Feb. 2025 Mar. 2025 Exchange Trading Volume (Million yen) 324,265 728,270 621,559 595,094 410,135 454,277 Marketplace Trading Volume (Million yen) 18,916 50,404 48,116 46,700 25,629 19,637 Customer Assets (Million yen) 735,675 1,106,754 1,142,223 1,285,614 873,795 859,623 Number of Verified Accounts 2,110,974 2,152,448 2,197,619 2,258,295 2,278,320 2,291,103 Apr. 2025 May. 2025 Jun. 2025 Jul. 2025 Aug. 2025 Sep. 2025 Exchange Trading Volume (Million yen) 366,050 375,676 310,449 387,980 318,293 243,193 Marketplace Trading Volume (Million yen) 21,672 21,333 18,525 39,165 29,146 26,358 Customer Assets (Million yen) 886,884 989,365 1,000,300 1,239,868 1,159,863 1,189,219 Number of Verified Accounts 2,302,376 2,325,978 2,351,223 2,378,672 2,400,859 2,421,080 Notes ● Exchange Trading Volume for a specific period is the total value, based on the underlying asset, of all transactions completed through Coincheck’s exchange platform. Coincheck’s exchange platform facilitates buy and sell transactions directly between two parties (a buyer and a seller) for which, generally, Coincheck charges no fee. Coincheck sometimes is a buyer on the exchange platform to help support transaction activity on the marketplace platform. ● Marketplace Trading Volume for a specific period is the total value, based on the underlying asset, of all transactions completed through Coincheck’s marketplace platform business. Historically, Coincheck’s total revenue has been derived primarily from transactions on Coincheck’s marketplace platform business. For additional details, please see Coincheck Group N.V.’s filings with the U.S. Securities and Exchange Commission. ● Customer Assets and Number of Verified Accounts correspond to figures as of the end of each month. Verified Accounts are all accounts that have been opened after the account owner completes all application procedures (including “know your customer” or “KYC”), after subtracting therefrom the total number of closed accounts. ● Customer Assets are cryptocurrencies held for customers + fiat currency deposited by customers on a Japanese generally accepted accounting principles (J-GAAP) basis. Customer Assets do not include non-fungible tokens (NFTs). ● Prior monthly numbers, which are generally preliminary at the time of initial publication, may have been updated by immaterial amounts.

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SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized. COINCHECK GROUP N.V. Date: October 02, 2025 By: /s/ Gary A. Simanson Name: Gary A. Simanson Title: Chief Executive Officer and President

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