Autumn has arrived in Tenshin and Yuuto is attending the prestigious Reimeikan girls’ school since his old school closed due to financial difficulties. He lives at a shrine, so he helps out occasionally. One day, he was asked to be an observer for a duel between two Tenjou sisters, Rio and Kikyou, to decide on who is deemed the successor of the family. However, there was an accident and somehow Rio ends up living with him.