Hitori Gotou is a high school girl who's starting to learn to play the guitar because she dreams of being in a band, but she's so shy that she hasn't made a single friend. However, her dream might come true after she meets Nijika Ijichi, a girl who plays drums and is looking for a new guitarist for her band.
Awakening her dormant abilities as a devil one day, Yuuko Yoshida aka Shadow Mistress Yuuko, is entrusted with the mission to defeat the Light clan's shrine maiden, a magical girl, by her ancestor Lilith. Yuuko meets magical girl Momo Chiyoda through her classmate Anri Sada, and challenges her to a duel, but loses quickly due to her lack of strength.
Since then, Yuuko has struggled with her role as a devil and her duel with Momo, and borrowed help from her regularly. However, by a strange coincidence, Yuuko also weakens Momo by taking away her power to cooperate in protecting the peace of Tama city.
Nervous to meet her new stepdad, Hiyori heads to the place she always feels at home—the ocean. When a curious girl named Koharu shows up, Hiyori decides to teach her how to fish, just like her father did before he died. But after Koharu reveals she’s also meeting her new family that night, the girls come to a startling realization. Their friendship is about to reach a whole new level!