Yuuto Amakawa lives on his own. His parents died in a car crash 7 years earlier and he has been looked after by his childhood friend, Rinko Kuzaki, and her family ever since then. The day of his 16th birthday is like any other, until an Ayakashi (demon) possesses the body of his friend and attempts to kill him. Yuuto is saved by a mysterious girl, Himari, who explains that he is a descendant from a line of demon-killers and is thus hated by demons. Now he has come of age the protective charm given by his grandmother has broken, and so Himari vows to protect him. Yuuto's eyes begin to water, but not from emotion; he is allergic to cats, and Himari happens to be a cat demon. Now Yuuta must try to stay alive; but if the demons don't get him, his allergies just might.