v3.26.1
Property and equipment (Details) - JPY (¥)
 12 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period ¥ 1,909,000,000 ¥ 1,973,000,000
Property, plant and equipment including right-of-use assets at end of period 1,464,000,000 1,909,000,000
Provisions made during the year 0 339,000,000
Property, plant and equipment, pledged as collateral 0 0
Leasehold improvements    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 338,000,000 3,000,000
Property, plant and equipment including right-of-use assets at end of period 241,000,000 338,000,000
Equipment and fixtures    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 32,000,000 24,000,000
Property, plant and equipment including right-of-use assets at end of period 92,000,000 32,000,000
Construction in progress    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 0 299,000,000
Property, plant and equipment including right-of-use assets at end of period 0 0
Total gross carrying amount    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 2,723,000,000 3,672,000,000
Additions 70,000,000 548,000,000
Additions (transferred from Construction in progress) 0 0
Additions (business combination) 27,000,000 2,000,000
Sales and disposals (3,000,000) (1,499,000,000)
Foreign currency translation 0  
Property, plant and equipment including right-of-use assets at end of period 2,817,000,000 2,723,000,000
Total gross carrying amount | Leasehold improvements    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 541,000,000 253,000,000
Property, plant and equipment including right-of-use assets at end of period 541,000,000 541,000,000
Total gross carrying amount | Equipment and fixtures    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 121,000,000 149,000,000
Property, plant and equipment including right-of-use assets at end of period 203,000,000 121,000,000
Total gross carrying amount | Construction in progress    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 0 299,000,000
Property, plant and equipment including right-of-use assets at end of period 0 0
Accumulated depreciation, amortisation and impairment    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period (815,000,000) (1,700,000,000)
Sales and disposals 3,000,000 1,496,000,000
Other 0  
Foreign currency translation 0  
Property, plant and equipment including right-of-use assets at end of period (1,355,000,000) (815,000,000)
Accumulated depreciation, amortisation and impairment | Profit or loss    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment (420,000,000) (511,000,000)
Accumulated depreciation, amortisation and impairment | Intangible assets other than goodwill    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment (122,000,000) (100,000,000)
Accumulated depreciation, amortisation and impairment | Leasehold improvements    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period (205,000,000) (250,000,000)
Property, plant and equipment including right-of-use assets at end of period (301,000,000) (205,000,000)
Accumulated depreciation, amortisation and impairment | Equipment and fixtures    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period (88,000,000) (125,000,000)
Property, plant and equipment including right-of-use assets at end of period (111,000,000) (88,000,000)
Accumulated depreciation, amortisation and impairment | Construction in progress    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 0 0
Property, plant and equipment including right-of-use assets at end of period 0 0
Right-of-use assets    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 1,539,000,000 1,647,000,000
Property, plant and equipment including right-of-use assets at end of period 1,131,000,000 1,539,000,000
Right-of-use assets | Total gross carrying amount    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period 2,061,000,000 2,972,000,000
Additions 0 418,000,000
Additions (transferred from Construction in progress) 0 0
Additions (business combination) 12,000,000 0
Sales and disposals 0 (1,329,000,000)
Foreign currency translation 0  
Property, plant and equipment including right-of-use assets at end of period 2,073,000,000 2,061,000,000
Right-of-use assets | Accumulated depreciation, amortisation and impairment    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Property, plant and equipment including right-of-use assets at beginning of period (522,000,000) (1,325,000,000)
Sales and disposals 0 1,329,000,000
Other 0  
Foreign currency translation 0  
Property, plant and equipment including right-of-use assets at end of period (943,000,000) (522,000,000)
Right-of-use assets | Accumulated depreciation, amortisation and impairment | Profit or loss    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment (299,000,000) (426,000,000)
Right-of-use assets | Accumulated depreciation, amortisation and impairment | Intangible assets other than goodwill    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment (122,000,000) (100,000,000)
Property, plant and equipment | Total gross carrying amount | Leasehold improvements    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Additions 0 3,000,000
Additions (transferred from Construction in progress) 0 406,000,000
Additions (business combination) 0 2,000,000
Sales and disposals 0 (122,000,000)
Foreign currency translation 0  
Property, plant and equipment | Total gross carrying amount | Equipment and fixtures    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Additions 70,000,000 7,000,000
Additions (transferred from Construction in progress) 0 13,000,000
Additions (business combination) 15,000,000 0
Sales and disposals (3,000,000) (48,000,000)
Foreign currency translation 0  
Property, plant and equipment | Total gross carrying amount | Construction in progress    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Additions 0 120,000,000
Additions (transferred from Construction in progress) 0 (419,000,000)
Additions (business combination) 0 0
Sales and disposals 0 0
Foreign currency translation 0  
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Leasehold improvements    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Sales and disposals 0 122,000,000
Other 0  
Foreign currency translation 0  
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Leasehold improvements | Profit or loss    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment (96,000,000) (77,000,000)
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Leasehold improvements | Intangible assets other than goodwill    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment 0 0
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Equipment and fixtures    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Sales and disposals 3,000,000 45,000,000
Other 0  
Foreign currency translation 0  
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Equipment and fixtures | Profit or loss    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment (26,000,000) (8,000,000)
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Equipment and fixtures | Intangible assets other than goodwill    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment 0 0
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Construction in progress    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Sales and disposals 0 0
Other 0  
Foreign currency translation 0  
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Construction in progress | Profit or loss    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment 0 0
Property, plant and equipment | Accumulated depreciation, amortisation and impairment | Construction in progress | Intangible assets other than goodwill    
Disclosure of reconciliation of changes in property, plant and equipment, including right-of-use assets [line items]    
Depreciation, property, plant and equipment ¥ 0 ¥ 0