Yuuto Amakawa lives a normal life until he's visited by a strange girl on his sixteenth birthday.

After going swimsuit shopping, Yuuto, Himari, and Rinko join their classmates at the beach, but a demon is lurking under the sea to kill Yuuto.

A water demon joins the crew; Himari gets a job at a maid cafe.

Yuuto goes back to his childhood home with Himari; Himari tries to help Yuuto recover his memories.

Yuuto learns about the magic he possesses along with the dangers; Yuto works to develop his powers.

A new Demon Slayer arrives but she's not looking for peace with demonkind, and she's claiming to be Yuuto's fiancé.