Yuuto Amakawa, who suffers from a severe allergy to cats, spends his mornings dealing with a runny nose caused by his friend Rinko's cat. However, on his sixteenth birthday, it is not just Rinko's pet that is aggravating his allergies (let alone his hormones)! Himari appears before him: a buxom, sword-wielding cat spirit in human form, who has sworn to protect Yuuto, who has now become the target of vengeful spirits! It is clear that Yuuto's allergies are the least of his problems — he will need Himari's help if he wants to survive until his seventeenth birthday!