Yuuto Amakawa is an orphaned child who comes from a long line of demon-slayers. It has been seven years ago since every living thing of his passed away. Up until now Yuuto has been able to continue to live a normal high school life thanks to a protective charm. However, on his sixteenth birthday the charm has worn off and demons have begun to sense his presence. Now that his life is in danger a mysterious catgirl named Himari appears.