Those with Momotarou and Oni blood in their veins have a long-standing rivalry. The Oni are reckless, impulsive, and chaotic, whereas the Momotarou safeguard the human world from the unruly Oni. Shiki Ichinose is a careless and irresponsible teen who knows he is defiant and is even proud of being expelled from school. Despite Shiki's rebellious streak, his foster father, Tsuyoshi, cares for him deeply. Tsuyoshi's selfless love is revealed in a sudden incident when a Momotarou bursts in searching for Shiki. Being a Momotarou himself, Tsuyoshi has hidden Shiki for years and kept his Oni heritage a secret, even from Shiki. As he sacrifices his life to save Shiki and reveals everything in his final moments, Shiki's Oni blood awakens for the first time, turning him into a wild monster brimming with rage and a desire for revenge. Shiki's brief outburst catches the eye of Naito Mudano, an Oni teacher at Rasetsu Academy—a school for young Oni who need to understand and refine their powers. Before Shiki can avenge his father, he must learn to control his stubborn and impulsive nature and, most importantly, battle his own demonic blood.