The bloodlines of "Oni" and "Momotaro" have been passed down through generations. Long ago, the Oni lived in seclusion, aware of their own cruelty. However, their peace was shattered by an invasion led by Momotaro. For thousands of years, these two factions formed the "Momotaro Agency" and the "Oni Agency," respectively, and have been in conflict ever since. Shiki Ichinose suddenly discovers his Oni heritage after an unexpected attack by Momotaro. This revelation sets Shiki on a path to discover the destiny inherent in his blood: a meeting with the Oni within him.