Shiki Ichinose is a hot-tempered teenager living with his adoptive father Tsuyoshi when an assassin attacks the two of them and forces the truth into the open. Shiki carries the blood of the Oni, and Tsuyoshi was once a Momotaro, one of the hunters sworn to wipe that bloodline out. Behind the old folktale lies a long war between the descendants of the Oni and the descendants of the peach boy who hunted them, and Shiki is dragged into it overnight.