This open-label, randomised, multicentre, phase 2 study (OHAI-NMIBC-01) compares toripalimab plus sequential intravesical gemcitabine followed by mitomycin C (GEM→MMC) with toripalimab alone in adults with BCG-unresponsive or BCG-intolerant high-risk non-muscle-invasive bladder cancer (HR-NMIBC). Two prespecified cohorts are analysed: (1) CIS cohort (CIS with/without Ta/T1) and (2) non-CIS cohort (high-risk Ta/T1 without CIS). In the combination arm, intravesical GEM→MMC is given weekly for 6 weeks (induction) and, for patients without recurrence at the first tumour assessment (\~month 3), monthly maintenance continues up to 24 months or until progression/unacceptable toxicity; toripalimab IV every 3 weeks starts during the first intravesical cycle and continues up to 24 months or until progression/unacceptable toxicity. The monotherapy arm receives toripalimab IV every 3 weeks up to 24 months or until progression/unacceptable toxicity. Cystoscopy and urine cytology are performed every 3 months; imaging every 24 weeks. Primary endpoints are 3-month complete response (CR) rate in the CIS cohort and median recurrence-free survival (RFS) in the non-CIS cohort. Secondary endpoints include landmark CR, PFS and OS, RFS/HG-RFS landmarks in the non-CIS cohort, and safety (CTCAE v5.0). Exploratory analyses will assess outcomes by protocol-defined PD-L1 status. Approximately 106 participants will be enrolled at multiple sites in China.