v3.25.2
Intangible assets (Details) - JPY (¥)
 12 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Disclosure of detailed information about intangible assets [line items]    
Intangible assets and goodwill at beginning of period ¥ 788,000,000 ¥ 601,000,000
Intangible assets and goodwill at end of period 2,401,000,000 788,000,000
Intangible assets pledged as security for liabilities 0 0
Internally generated intangible assets    
Disclosure of detailed information about intangible assets [line items]    
Intangible assets and goodwill at beginning of period 788,000,000 600,000,000
Intangible assets and goodwill at end of period 1,161,000,000 788,000,000
Goodwill | Not internally generated    
Disclosure of detailed information about intangible assets [line items]    
Intangible assets and goodwill at beginning of period 0 0
Intangible assets and goodwill at end of period 1,240,000,000 0
Others | Not internally generated    
Disclosure of detailed information about intangible assets [line items]    
Intangible assets and goodwill at beginning of period 0 0
Intangible assets and goodwill at end of period 0 0
Gross carrying amount    
Disclosure of detailed information about intangible assets [line items]    
Intangible assets and goodwill at beginning of period 1,331,000,000 965,000,000
Additions (not by business combination) 524,000,000 380,000,000
Additions (transferred from property and equipment) 100,000,000 25,000,000
Additions (business combination) 1,240,000,000  
Sales and disposals (36,000,000) (39,000,000)
Intangible assets and goodwill at end of period 3,159,000,000 1,331,000,000
Gross carrying amount | Internally generated intangible assets    
Disclosure of detailed information about intangible assets [line items]    
Intangible assets and goodwill at beginning of period 1,328,000,000 962,000,000
Additions (not by business combination) 524,000,000 380,000,000
Additions (transferred from property and equipment) 100,000,000 25,000,000
Additions (business combination) 0  
Sales and disposals (35,000,000) (39,000,000)
Intangible assets and goodwill at end of period 1,917,000,000 1,328,000,000
Gross carrying amount | Goodwill | Not internally generated    
Disclosure of detailed information about intangible assets [line items]    
Intangible assets and goodwill at beginning of period 0 0
Additions (not by business combination) 0 0
Additions (transferred from property and equipment) 0 0
Additions (business combination) 1,240,000,000  
Sales and disposals 0 0
Intangible assets and goodwill at end of period 1,240,000,000 0
Gross carrying amount | Others | Not internally generated    
Disclosure of detailed information about intangible assets [line items]    
Intangible assets and goodwill at beginning of period 3,000,000 3,000,000
Additions (not by business combination) 0 0
Additions (transferred from property and equipment) 0 0
Additions (business combination) 0  
Sales and disposals (1,000,000) 0
Intangible assets and goodwill at end of period 2,000,000 3,000,000
Accumulated depreciation and amortisation    
Disclosure of detailed information about intangible assets [line items]    
Intangible assets and goodwill at beginning of period (544,000,000) (365,000,000)
Sales and disposals 2,000,000  
Amortisation (217,000,000) (179,000,000)
Intangible assets and goodwill at end of period (759,000,000) (544,000,000)
Accumulated depreciation and amortisation | Internally generated intangible assets    
Disclosure of detailed information about intangible assets [line items]    
Intangible assets and goodwill at beginning of period (541,000,000) (362,000,000)
Sales and disposals 1,000,000  
Amortisation (217,000,000) (178,000,000)
Intangible assets and goodwill at end of period (757,000,000) (541,000,000)
Accumulated depreciation and amortisation | Goodwill | Not internally generated    
Disclosure of detailed information about intangible assets [line items]    
Intangible assets and goodwill at beginning of period 0 0
Sales and disposals 0  
Amortisation 0 0
Intangible assets and goodwill at end of period 0 0
Accumulated depreciation and amortisation | Others | Not internally generated    
Disclosure of detailed information about intangible assets [line items]    
Intangible assets and goodwill at beginning of period (3,000,000) (3,000,000)
Sales and disposals 1,000,000  
Amortisation 0 0
Intangible assets and goodwill at end of period ¥ (2,000,000) ¥ (3,000,000)