v3.25.2
Fair value measurement - Fair value hierarchy of assets and liabilities measured at fair value (Details) - JPY (¥)
¥ in Millions
Mar. 31, 2025
Mar. 31, 2024
Apr. 01, 2023
 [1]
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total assets ¥ 112,274 ¥ 119,189 [1] ¥ 71,978
Total Liabilities 101,505 106,745 [1] ¥ 61,501
Recurring      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total assets 44,748 44,251  
Total Liabilities 44,889 44,021  
Recurring | Crypto Borrowings      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total Liabilities 44,479 44,020  
Recurring | Derivatives      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total Liabilities   1  
Recurring | Public Warrants      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total Liabilities 398    
Recurring | Private Warrants      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total Liabilities 12    
Recurring | Cryptocurrencies      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total assets 44,680 44,207  
Recurring | Derivatives      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total assets 68 44  
Recurring | Level 1      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total assets 44,702 44,209  
Total Liabilities 44,878 44,020  
Recurring | Level 1 | Crypto Borrowings      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total Liabilities 44,479 44,020  
Recurring | Level 1 | Derivatives      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total Liabilities   0  
Recurring | Level 1 | Public Warrants      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total Liabilities 398    
Recurring | Level 1 | Private Warrants      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total Liabilities 0    
Recurring | Level 1 | Cryptocurrencies      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total assets 44,680 44,207  
Recurring | Level 1 | Derivatives      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total assets 22 2  
Recurring | Level 2      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total assets 0 3  
Total Liabilities 0 1  
Recurring | Level 2 | Crypto Borrowings      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total Liabilities 0 0  
Recurring | Level 2 | Derivatives      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total Liabilities   1  
Recurring | Level 2 | Public Warrants      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total Liabilities 0    
Recurring | Level 2 | Private Warrants      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total Liabilities 0    
Recurring | Level 2 | Cryptocurrencies      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total assets 0 0  
Recurring | Level 2 | Derivatives      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total assets 0 3  
Recurring | Level 3      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total assets 46 39  
Total Liabilities 12 0  
Recurring | Level 3 | Crypto Borrowings      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total Liabilities 0 0  
Recurring | Level 3 | Derivatives      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total Liabilities   0  
Recurring | Level 3 | Public Warrants      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total Liabilities 0    
Recurring | Level 3 | Private Warrants      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total Liabilities 12    
Recurring | Level 3 | Cryptocurrencies      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total assets 0 0  
Recurring | Level 3 | Derivatives      
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]      
Total assets ¥ 46 ¥ 39  
[1] The comparative information is restated due to change in accounting policy. See Note 2 (5) “Changes in