Amaumi Haruhiko is a high school student attending Shimano Academy in the town of Narasakicho. Narasakicho is home to a mysterious rainbow that constantly overlooks the town and is connected to granting a magical wish known as "Gift." Gift is a once-in-a-lifetime present exchanged between two people. As a child, Haruhiko was close to his childhood friend, Kirino, until he gained a new non-blood sister named Riko. Haruhiko developed a strong bond with Riko until they sadly parted ways because Haruhiko's father could no longer support both of them. After some time has passed, Riko finally returns to Narasakicho and, along with Kirino, begins attending Shimano Academy with Haruhiko. The series focuses on the relationships among these main protagonists and gradually reveals the story behind both Gift and the rainbow.