Contract liabilities (Details)	6 Months Ended
Jun. 30, 2026 USD ($)	Jun. 30, 2026 JPY (¥)	Jun. 30, 2025 JPY (¥)
Revenue from Contract with Customer [Abstract]
Beginning balance	$ 1,026,333	¥ 166,892,068	¥ 158,243,945
Deposits received from customers	3,289,444	534,896,463	527,425,898
Amounts recognized to revenue	(1,985,951)	(322,935,511)	(309,351,064)
Less: refunds to customers			(130,000)
Less: refunds to customers			130,000
Ending balance	$ 2,329,826	¥ 378,853,020	¥ 376,188,779

Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-11

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479837/606-10-45-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479806/606-10-50-8

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479837/606-10-45-2

Name:	us-gaap_ContractWithCustomerLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant