Having lived in an orphanage for as long as he can remember, high school student Yuki Sakurai has always believed that he existed to burden others. Despite possessing a mysterious power that allows him to see other people's emotions, the ability seems to torment him instead.

One day, a beautiful man in black clothes saves Yuki's life, and Yuki faintly feels as if he has met this stranger before. The stranger, later introducing himself as Zess, displays a strong concern about Yuki but quickly disappears after giving him a warning. The following day, Takashiro Giou—the head of the Giou Clan—appears at the orphanage claiming to be Yuki's brother and proposes an idea that Yuki is reluctant to accept.

As puzzling problems threaten his safety emerge and familiar faces reappear, Yuki soon learns that his frail existence holds a greater significance than he had initially thought.