In the town of Narasakicho, high school student Amaumi Haruhiko experiences the mystical phenomenon of an enigmatic rainbow that grants a rare magical wish known as 'Gift.' This peculiar occurrence binds individuals in a unique connection. Haruhiko, once inseparable from childhood friend Kirino, finds his world reshaped when a new non-blood sister named Riko enters his life. Their bond deepens until circumstances force them apart. However, fate reunites them in Narasakicho, where they join Shimano Academy together. As the trio navigates their intertwined relationships, the secrets of Gift and the mysterious rainbow gradually unfold, shaping their intertwined destinies.