Kazuki's parents often traveled abroad, so he was raised most of the time with the Tokizawas, distant relatives of his. There he was raised like a son along with Hazuki, the Tokizawa's daughter. However, his peaceful life is about to be shattered when, while he's staying with the Tokizawas during his parents' long business trip, a mysterious girl called Momoka appears and says she will "protect Kazuki's life".