Masaharu Uchiyama focused on enhancing data integrity and consistency in authentication flows by addressing soft-delete support across the supabase/auth-js and supabase/supabase-js repositories. He updated the User interface in both libraries to include a deleted_at property, ensuring that soft deletion states were accurately reflected and handled throughout the authentication modules. Working primarily with TypeScript, he applied skills in API integration and interface definition to standardize data shapes and reduce model drift between client libraries. This targeted work improved the reliability and testability of authentication state management, demonstrating careful attention to cross-repository consistency and backend alignment within a short timeframe.