Yuuto Amakawa has a very typical existence in the city after the loss of his parents. His cat allergies are the only thing he has to worry about while attending school with Rinko, his next-door neighbor. This all changes on his sixteenth birthday, when an Ayakashi—a supernatural creature—attacks him for his ancestors' misdeeds. Himari, a mystery cat-woman with a sword, saves him and reveals that Yuuto is the scion of a line of demon-slayers, and she is there to guard him now that the enchantment that has kept him concealed from the magical powers of the world has lost its effectiveness.