The focus of the story is on Akira Nikaido, an average, lazy high school student leading a mundane life until he meets the enigmatic Shirogane, who insists they share a destiny. Initially doubtful, Akira is surprised by Shirogane's claims. One evening, Akira's friend Aya asks him for help locating an item she left at school. While searching, a shadow monster attacks Akira. Shirogane points out that this incident disrupted the balance between the human and shadow realms. As a result, Akira must transform into a "shin," a creature from the shadow realm, to restore order. The anime version includes shonen-ai elements that the original manga lacks.