Seven years ago, Yuto Amakawa's parents died in a car accident, leaving him alone without a single relative, the only item left of his family being a strange and mysterious amulet given to him by his late grandmother. Ever since then, his childhood friend Rinko Kuzaki (and her parents[ch. 1]) has cooked for and taken care of him. His life takes a drastic turn on his 16th birthday when he meets Himari, a cat demon samurai girl. Himari reveals to him that some of his ancestors were part of the twelve Demon Slayer families that have been slaying demons since the feudal era. She has sworn an oath to protect Yuto from the demons that are out to kill him, but Yuto's allergy to cats makes it somewhat difficult to deal with. Later on, Yuto encounters various girls who take a liking to him: Shizuku, a mizuchi in the form of a small child; Lizlet, a tsukumogami in the form of a busty tea-serving maid; and Kuesu, another Demon Slayer who is revealed to be Yuto's fiancée and an object of Yuto's lost past. As the series progresses, Yuto and the group encounter some powerful ayakashi, with some of them being allies, and Yuto eventually makes a life-changing decision to fight for his belief of coexistence between human and ayakashi.