Company: CNCKW
Filing Date: 2025-08-05
Form Type: 6-K
Source: 0001628280-25-037615
Chunk: 0

Company: Coincheck Group N.V.
Filing Date: 2025-08-05
Form: 6-K
Chunk 0
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### 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 August 2025

#### Commission File Number: 001-42438

#### COINCHECK GROUP N.V.
<div align='center'>(Translation of registrant’s name into English)</div>

#### Nieuwezijds Voorburgwal 162

#### 1012 SJ Amsterdam

#### The Netherlands
<div align='center'>(Address of principal executive offices)</div>

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F:

<div align='center'>Form 20-F ☒ Form 40-F ☐</div>

On August 5, 2025, Coincheck Group N.V. issued a press release announcing a strategic business relationship between Coincheck Inc. and Mercoin, which is furnished as Exhibit 99.1 to this Report on Form 6-K.

### EXHIBIT INDEX
<div align='center'>1</div>

### 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.

| Date: August 05, 2025 |     | COINCHECK GROUP N.V. 
 By:                  |     | /s/ Gary A. Simanson |     |                                       |
|:----------------------|:----|:---------------------|:----|:---------------------|:----|:--------------------------------------|
|                       |     |                      |     | Name:                |     | Gary A. Simanson                      |
|                       |     |                      |     | Title:               |     | Chief Executive Officer and President |

<div align='center'>2</div>