Akira Nikaidou is a typical slacker high school student who believes he leads a normal life until a mysterious man named Shirogane appears and instructs him to meet at the school that night. Although skeptical, Akira goes anyway... and is attacked by a shadow monster! Shirogane convinces him 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, to help restore that balance.