For hundreds of years, the descendants of, or what are now called, the Oni Organization and Momotaro have been killing each other due to an unspecified agreement. Since the great war three years ago between the Oni Organization and Momotaro, which resulted in an equal outcome and ended with an agreement to divide their respective territories, no Oni has harmed humans again. Three years have passed, and everything is now safe, although Momotaro and the Oni have a shadowy presence among the city's residents, especially since their powers are not visible to ordinary people. Both organizations are relatively safe for now.

Ryu Shiranui, captain of the Oni Organization's combat unit, Unit 17 in Tokyo. He has a dark and painful past. His mother and older sister were killed by his biological father because he was a Momotaro, but that was all years ago. While living with the Oni Organization, he met a girl, the vice-captain of the reconnaissance unit in one of the Oni Organization's areas in Tokyo. until now they are quite close, sometimes working together to find rampaging oni, especially since Ryu seems to like the girl (even though it is not visible and never wants to admit it) his arrogant and stubborn nature, especially he thinks he lives only to fight and take revenge on his father.

until one day they go on a mission because there is a rampaging oni, again Ryu not only goes with his deputy, he also asks for the help of the scout girl.