Yuuto Amakawa, plagued by severe feline allergies, faces daily struggles with his friend Rinko's cat. However, everything changes on his sixteenth birthday when he encounters Himari, a voluptuous cat spirit wielding a sword in human form. Himari pledges to defend Yuuto, who becomes the focal point of vengeful spirits. Amidst his allergy woes and hormonal stirrings, Yuuto realizes he must rely on Himari's protection to survive until his seventeenth birthday.