When Yuuto's parents died, his childhood friend Rinko stepped in to take care of him. But on Yuuto's sixteenth birthday, another girl barges into his life-a sword-wielding cat-girl warrior named Himari who talks like she just arrived from ancient Japan. She is actually a supernatural guardian summoned by Yuuto's grandparents to protect him. Besides the obvious problem of living with a buxom cat-girl, Yuuto is allergic to cats!