The narrative centers on Akira Nikaido, a high school student and typical slacker leading an ordinary existence. This changes when he encounters the enigmatic Shirogane, a man who abruptly appears and claims they share a destined connection. Akira is taken aback and dismisses the assertion entirely. One night, Akira’s friend Aya forgets an item at school and requests his assistance in retrieving it. He consents, but during the visit, he is assaulted by a shadow monster. Shirogane persuades him that the equilibrium between the human realm and the shadow realm has been disrupted, and that Akira must transform into a "shin"—a being of the shadow world—to aid in restoring that balance. The anime incorporates shonen-ai elements that are entirely missing from the manga.