Ryūji Kisaragi is a normal high school boy whose peaceful life is turned into an adventure by the return of his second cousin Eriko Nanao. Ryūji and Eriko seize a relic box from a black broker, and in the box they find Rose, a red dragon girl. In order to protect Rose from the black organization, Ryuji decides to fight using his power as a relic handler.
Based off the Japanese folktale "Momotaro", a girl named Momoko was born inside a giant peach. She was adopted by an old couple and grew up to be a voluptuous teen. Her three friends are animal Gods Inukami (dog), Sarukami (monkey), and Kijigami (pheasant); she has the ability to fuse with any of them to become a powerful magical girl. One day Momoko's village is attacked by the demon king's army who are searching for fragments of a treasure used to protect the land. After defeating the demons Momoko embarks on an journey with her animal friends to search for the "peach fragments" before they fall into the wrong hands.