Kujo Saburou is an "ordinary" high schooler, hyperactive and strangely interested in mysterious (alien) things. He quickly becomes friends with a new transfer student, Shima Ango, who happens to find him in a game of hide-and-seek. But what he doesn't know is Shima's true goal: the extermination of mononoke terrorizing the Tokyo area. Caught in the middle of their fight, Kujo loses his head, unsealing an Oni inside of him...