Yuuto Amakawa lives a normal life until he's visited by a strange girl on his sixteenth birthday. Beautiful cat spirit samurai Himari tells him about his family's heritage as demon slayers.

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.

Water demon Shizuku decides to live with Yuuto and the others, making Himari fell bad about her domestic skills. Himari gets a job at a local café as a cat-eared maid, but there's something off about the lead waitress.

Yuuto goes back to his childhood home with Himari, but the current caretaker isn't exactly welcoming; demons attack while Himari tries to jog Yuuto's memories.

Yuuto learns about the magic he possesses along with the dangers of Himari losing herself to bloodlust. He works on developing his powers to keep this from happening.

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