At Shimano Academy in Narasakicho, Haruhiko is a student with a fascination for an enigmatic rainbow in town that possesses the power to grant two individuals their "Gift" wish. During his childhood, Haruhiko and his best friend Kirino were inseparable, until his new stepsister Riko emerged into his life. However, due to financial difficulties, Haruhiko and Riko were separated until she unexpectedly returned to Narasakicho after years and enrolled at Shimano Academy alongside Kirino and Haruhiko. As the trio's bond strengthens, they unravel the mysterious origins of the rainbow and unravel the secrets of the elusive Gift.