v3.25.2
Financial risk management - Maturity analysis for financial assets held for managing liquidity risk (Details) - JPY (¥)
¥ in Millions
Mar. 31, 2025
Mar. 31, 2024
Apr. 01, 2023
 [1]
Mar. 31, 2022
 [1]
Other Financial Liabilities [Abstract]        
Crypto asset borrowings ¥ 44,479 ¥ 44,020 [1] ¥ 18,756  
Borrowing 751 0    
Lease liabilities 1,277 1,661    
Derivative financial liabilities 0 1    
Other 1,699 821    
Total 3,727 2,483    
Cash and cash equivalents 8,584 10,837 [1] 7,697 ¥ 17,704
Crypto assets held 44,680 44,207 [1] ¥ 18,969  
Contractual cash flows        
Other Financial Liabilities [Abstract]        
Crypto asset borrowings 44,479 44,020    
Borrowing 751      
Lease liabilities 1,293 1,687    
Derivative financial liabilities 0 1    
Other 1,699 821    
Total 3,743 2,509    
Cash and cash equivalents 8,584 10,837    
Crypto assets held 44,680 44,207    
Within one year        
Other Financial Liabilities [Abstract]        
Crypto asset borrowings 44,479 44,020    
Borrowing 751      
Lease liabilities 384 394    
Derivative financial liabilities 0 1    
Other 1,699 821    
Total 2,834 1,216    
Cash and cash equivalents 8,584 10,837    
Crypto assets held 44,680 44,207    
From one year to two years        
Other Financial Liabilities [Abstract]        
Crypto asset borrowings 0 0    
Borrowing 0      
Lease liabilities 356 384    
Derivative financial liabilities 0 0    
Other 0 0    
Total 356 384    
Cash and cash equivalents 0 0    
Crypto assets held 0 0    
From two years to three years        
Other Financial Liabilities [Abstract]        
Crypto asset borrowings 0 0    
Borrowing 0      
Lease liabilities 356 356    
Derivative financial liabilities 0 0    
Other 0 0    
Total 356 356    
Cash and cash equivalents 0 0    
Crypto assets held 0 0    
From three years to four years        
Other Financial Liabilities [Abstract]        
Crypto asset borrowings 0 0    
Borrowing 0      
Lease liabilities 197 356    
Derivative financial liabilities 0 0    
Other 0 0    
Total 197 356    
Cash and cash equivalents 0 0    
Crypto assets held 0 0    
From four years to five years        
Other Financial Liabilities [Abstract]        
Crypto asset borrowings 0 0    
Borrowing 0      
Lease liabilities 0 197    
Derivative financial liabilities 0 0    
Other 0 0    
Total 0 197    
Cash and cash equivalents 0 0    
Crypto assets held 0 0    
More than five years        
Other Financial Liabilities [Abstract]        
Crypto asset borrowings 0 0    
Borrowing 0      
Lease liabilities 0 0    
Derivative financial liabilities 0 0    
Other 0 0    
Total 0 0    
Cash and cash equivalents 0 0    
Crypto assets held ¥ 0 ¥ 0    
[1] The comparative information is restated due to change in accounting policy. See Note 2 (5) “Changes in