v3.26.1
Fair value measurement - Fair value hierarchy of assets and liabilities measured at fair value (Details) - JPY (¥)
¥ in Millions
Mar. 31, 2026
Mar. 31, 2025
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Assets ¥ 117,121 ¥ 112,353
Liabilities 95,375 101,584
Recurring    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Assets 38,040 44,748
Liabilities 37,676 44,889
Recurring | Crypto asset borrowings    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Liabilities 37,543 44,479
Recurring | Public warrant liabilities    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Liabilities 128 398
Recurring | Private warrant liabilities    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Liabilities 4 12
Recurring | Cryptocurrencies    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Assets 37,876 44,680
Recurring | Derivatives    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Assets 164 68
Recurring | Level 1    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Assets 37,986 44,702
Liabilities 37,672 44,878
Recurring | Level 1 | Crypto asset borrowings    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Liabilities 37,543 44,479
Recurring | Level 1 | Public warrant liabilities    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Liabilities 128 398
Recurring | Level 1 | Private warrant liabilities    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Liabilities 0 0
Recurring | Level 1 | Cryptocurrencies    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Assets 37,876 44,680
Recurring | Level 1 | Derivatives    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Assets 110 22
Recurring | Level 2    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Assets 0 0
Liabilities 0 0
Recurring | Level 2 | Crypto asset borrowings    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Liabilities 0 0
Recurring | Level 2 | Public warrant liabilities    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Liabilities 0 0
Recurring | Level 2 | Private warrant liabilities    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Liabilities 0 0
Recurring | Level 2 | Cryptocurrencies    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Assets 0 0
Recurring | Level 2 | Derivatives    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Assets 0 0
Recurring | Level 3    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Assets 54 46
Liabilities 4 12
Recurring | Level 3 | Crypto asset borrowings    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Liabilities 0 0
Recurring | Level 3 | Public warrant liabilities    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Liabilities 0 0
Recurring | Level 3 | Private warrant liabilities    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Liabilities 4 12
Recurring | Level 3 | Cryptocurrencies    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Assets 0 0
Recurring | Level 3 | Derivatives    
Disclosure Of Significant Unobservable Inputs Used In Fair Value Measurement Of Assets and Liabilities [Line Items]    
Assets ¥ 54 ¥ 46