Gift: Eternal Rainbow

Amaumi Haruhiko is a high school student at Shimano Academy in Narasakicho, a town with a mysterious rainbow that hangs in the sky. The rainbow is said to be connected to a magical wish called "Gift," which is a unique bond between two people that can only be experienced once in a lifetime. Haruhiko's life is complicated by the arrival of Riko, his non-blood sister, and her departure after Haruhiko's father is no longer able to support them.