The slapstick romantic comedy centers around an ordinary 16-year-old high school boy named Yuto Amakawa who is protected by a spirit - specifically, a beautiful, sword-wielding cat girl spirit named Himari. Yuto is descended from a family that has subjugated demons since time immemorial. The charm that once protected him is now impotent, but fortunately, at that same moment, Himari appears before him as his new guardian.
Seven years ago, Amakawa Yuuto's parents died leaving him living alone without a single relative. Ever since then, his childhood friend, Kuzaki Rinko, has woken him up, cooked for him and generally taken care of him. The only thing he has from any relative is a mysterious charm, a red ball, given to him by his grandparents as a good luck charm (an omamori).
On the day of his 16th birthday, this charm mysteriously disappears, and into Yuuto's life walks Himari. A cat spirit-samurai girl and demon hunter who swears to protect Yuuto. There is only one small problem. Yuuto has a severe allergic reaction to cats! Hang on to your manga-reading chair as this slapstick love comedy with a bit of good ol' fashion demon hunting is about to begin!