Kyouko Fudatsuki may be a real beauty at her school, but her brother, Kenji, will not tolerate anyone showing the slightest interest in her. Although Kenji seems to be obsessed with his sister, he only wants to protect her.

Unbeknownst to all, Kyouko is a jiangshi; when her hair comes loose, she loses self-control and sucks the blood out of anyone she crosses paths with. To avoid attacking innocent people, she must consume blood daily and wear a special hair ribbon at all times. As he diligently watches over his sister's necessities, Kenji faces an additional challenge—Kyouko's outbursts drastically change her demeanor, making it difficult for him to understand her true feelings.