Gift: eternal rainbow

Amaumi Haruhiko is a high school student who attends Shimano Academy in a town called Narasakicho. Narasakicho contains an unknown rainbow which constantly overlooks the town and is related to granting a magical wish called "Gift". Gift is a once-in-a-lifetime present between two people. As a child, Haruhiko has been close with his childhood friend, Kirino, until he obtains a new non-blood sister...