Postdoctoral Project Researcher position in Experimental Particle Physics focusing on vertex detector operation, upgrade R&D, and data analysis for the Belle II experiment. The role includes detector development (sensor, mechanics, and readout systems) and collaborative research within an international team. The appointment is annually renewable, with funding through a national KAKENHI project, and may continue until March 31, 2029. The position requires at least six months of research at an overseas partner institute and offers opportunities for career development within Japan’s high-energy physics community.