Shin Meiwa, inspired by the success with their PS/US-1, had several commercial amphibian designs on the drawing board offering improved seaworthiness (i.e. the ability to takeoff and land on rough waters) over existing designs, thus promising a degree of serviceability as a seaplane that closely approaches that of land-based aircraft.
SS-X, also known as the Shin Meiwa LA (Light Amphibian), is one of these designs and a "40-passenger light amphibian for inter-island feeder service".