v3.26.1
Income taxes - Schedule of reconciliation between statutory rate and the Group's effective tax rate (Details)
12 Months Ended
Dec. 31, 2025
CNY (¥)
Dec. 31, 2025
USD ($)
Dec. 31, 2024
CNY (¥)
Dec. 31, 2023
CNY (¥)
Income taxes        
Income before provision for income tax ¥ 1,254,504 $ 179,392 ¥ (287,402,606) ¥ 68,197,344
Income taxes, reconciliation, amount        
Tax rate differential 8,759      
Changes in valuation allowances (4,634)      
Nondeductible items 4,739,972      
True-up (3,881,972)      
Effect of expired tax loss 665,217      
Disposal of previously recognized tax loss 1,137,971      
Effective tax rate ¥ 28,408,570 $ 4,062,372 ¥ 15,406,551 ¥ 1,068,958
Tax Jurisdiction of Domicile [Extensible Enumeration] PRC PRC    
Income taxes, reconciliation, percent        
Local Income tax of mainland of China     25.00% 25.00%
Tax rate differential 0.70% 0.70% 20.76% (77.33%)
Changes in valuation allowances (0.37%) (0.37%) (42.33%) 36.13%
Nondeductible items 377.84% 377.84% (8.79%) 19.77%
True-up (309.44%) (309.44%)    
Effect of expired tax loss 53.03% 53.03%    
Disposal of previously recognized tax loss 90.70% 90.70%    
Effective tax rate 2264.53% 2264.53% (5.36%) 3.57%
PRC        
Income taxes, reconciliation, amount        
Local Income tax of mainland of China ¥ 313,626      
Changes in valuation allowances ¥ 11,727,719      
Income taxes, reconciliation, percent        
Local Income tax of mainland of China 25.00% 25.00%    
Changes in valuation allowances 934.85% 934.85%    
Cayman        
Income taxes, reconciliation, amount        
Tax rate differential ¥ (2,598,393)      
Income taxes, reconciliation, percent        
Tax rate differential (207.12%) (207.12%)    
British Virgin Islands ("BVI")        
Income taxes, reconciliation, amount        
Tax rate differential ¥ 16,300,305      
Income taxes, reconciliation, percent        
Tax rate differential 1299.34% 1299.34%