Notes - Segment Information
| Concept | 2023-10-01 to 2023-12-31 | As at 2023-12-31 | 2023-10-01 to 2023-12-31 | 2023-10-01 to 2023-12-31 | 2023-10-01 to 2023-12-31 | 2023-10-01 to 2023-12-31 | 2023-10-01 to 2023-12-31 | As at 2023-09-30 | 2022-10-01 to 2022-12-31 | 2022-10-01 to 2022-12-31 | 2022-10-01 to 2022-12-31 | 2022-10-01 to 2022-12-31 | 2022-10-01 to 2022-12-31 | 2022-10-01 to 2022-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Notes - Segment information | ||||||||||||||
| Segment information | ||||||||||||||
| Revenue | ||||||||||||||
| Revenue from external customers | 
                                                569,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                8,190,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                8,190,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,093,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,527,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                622,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,497,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                7,583,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,463,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                7,583,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Intersegment revenue | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -1,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -2,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Revenue | 
                                                569,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                8,190,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                8,191,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,093,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -1,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,528,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                622,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                5,499,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                7,585,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -2,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,463,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                7,583,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Segment profit (loss) | 
                                                -100,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -5,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -9,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -605,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                695,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -113,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                599,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                280,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -206,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                282,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Other income and expenses, net | — | — | 
                                                -46,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                539,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Finance income and costs, net | — | — | 
                                                -43,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                -15,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Share of profit (loss) of investments accounted for using equity method | — | — | 
                                                -35,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                -70,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Profit (loss) before tax | — | — | 
                                                -131,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | 
                                                737,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Assets | — | 
                                                48,291,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                51,153,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
| Investments accounted for using equity method | — | 
                                                624,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | 
                                                536,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | 
| Depreciation and amortization | 
                                                11,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                495,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                495,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                210,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                272,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                20,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                285,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                488,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                182,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                488,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             |