The story centers on high‑school student Akira Nikaido, a typical slacker living an ordinary life. His routine is disrupted when he encounters Shirogane, a mysterious man who suddenly appears and claims that the two of them share a destiny. Akira is shocked and refuses to believe the claim. One night, his friend Aya forgets something at school and asks Akira to help her retrieve it. He agrees, but while they search, Akira is attacked by a shadow monster. Shirogane explains that the balance between the human world and the shadow world has been distorted, and that Akira must become a “shin”, a creature of the shadow world, in order to restore equilibrium. The anime contains shonen‑ai themes.