Quarterly Balance Sheet
| Concept | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2023-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2022-12-31 | As at 2021-12-31 | As at 2021-12-31 | As at 2021-12-31 | As at 2021-12-31 | As at 2021-12-31 | As at 2021-12-31 | As at 2021-12-31 | As at 2021-12-31 | As at 2021-12-31 | 
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Quarterly balance sheet | |||||||||||||||||||||||||||||||||||
| Balance sheet | |||||||||||||||||||||||||||||||||||
| Assets | |||||||||||||||||||||||||||||||||||
| Current assets | |||||||||||||||||||||||||||||||||||
| Cash and deposits | — | — | — | 
                                                1,325,554,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,727,270,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Work in process | — | — | — | 
                                                1,644,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,151,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Inventories | — | — | — | 
                                                64,107,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                71,478,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | — | — | — | 
                                                849,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                3,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Current assets | — | — | — | 
                                                1,629,396,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,092,166,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current assets | |||||||||||||||||||||||||||||||||||
| Property, plant and equipment | — | — | — | 
                                                1,166,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,437,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Property, plant and equipment | |||||||||||||||||||||||||||||||||||
| Machinery and equipment | — | — | — | 
                                                233,509,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                254,610,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Accumulated depreciation | — | — | — | 
                                                -232,343,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -252,173,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Machinery and equipment, net | — | — | — | 
                                                1,166,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,437,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Tools, furniture and fixtures | — | — | — | 
                                                85,451,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                97,024,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Accumulated depreciation | — | — | — | 
                                                -85,451,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -97,024,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Tools, furniture and fixtures, net | — | — | — | 
                                                0
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                0
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Investments and other assets | — | — | — | 
                                                120,892,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                120,866,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Investments and other assets | |||||||||||||||||||||||||||||||||||
| Long-term prepaid expenses | — | — | — | 
                                                8,081,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                8,055,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Other | — | — | — | 
                                                0
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                0
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current assets | — | — | — | 
                                                122,058,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                123,303,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Assets | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,751,454,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,751,454,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,215,470,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,215,470,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | 
                                                
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | 
| Liabilities | |||||||||||||||||||||||||||||||||||
| Current liabilities | |||||||||||||||||||||||||||||||||||
| Short-term borrowings | — | — | — | 
                                                291,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                184,000,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Income taxes payable | — | — | — | 
                                                23,952,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                23,943,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Current liabilities | — | — | — | 
                                                539,038,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                370,455,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current liabilities | |||||||||||||||||||||||||||||||||||
| Asset retirement obligations | — | — | — | 
                                                54,692,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                54,268,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Non-current liabilities | — | — | — | 
                                                54,692,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                54,268,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Liabilities | — | — | — | 
                                                593,731,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                424,724,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Net assets | |||||||||||||||||||||||||||||||||||
| Shareholders' equity | |||||||||||||||||||||||||||||||||||
| Share capital | — | — | — | 
                                                2,388,422,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,097,017,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Capital surplus | — | — | — | 
                                                3,988,202,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                3,696,798,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Retained earnings | — | — | — | 
                                                -5,236,350,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -4,016,331,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Treasury shares | — | — | — | 
                                                -292,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                -292,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Shareholders' equity | — | — | — | 
                                                1,139,981,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                1,777,192,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Share acquisition rights | — | — | — | 
                                                17,741,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                13,554,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 
| Net assets | 
                                                17,741,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                2,388,422,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                1,157,723,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -5,236,350,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,139,981,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,988,202,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,988,202,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                -292,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -5,236,350,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                -4,016,331,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -292,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,790,746,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,696,798,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,696,798,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,777,192,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | 
                                                2,097,017,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -4,016,331,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                13,554,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | 
                                                35,394,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -2,773,693,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -292,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,893,049,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,515,929,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                -2,773,693,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,115,710,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                3,115,710,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
                                                1,857,654,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | 
| Liabilities and net assets | — | — | — | 
                                                1,751,454,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | 
                                                2,215,470,000
                                                
                                                    
                                                        JPY
                                                    
                                                
                                             | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — |