Since the death of his parents, Ajiro Shinpei has lived with the Kofune family and their two daughters, Mio and Ushio. Yet at one stage in his life he left his home island to pursue his education in Tokyo. Shinpei returns after Ushio tragically drowns while trying to rescue Shiori, the daughter of the owners of a nearby store. During the funeral, his best friend informs him of bruises found around Ushio's neck, casting doubt on the cause of her death.
