Unlike her family, Karin Maaka is a vampire who walks outside during the day and sleeps during the night. Nobody from her town knows of her true identity—and she plans to keep it that way, as it could jeopardize her "normal" life if someone were to find out.

Kenta Usui witnesses Karin bite someone on the day he transfers into her class as a new student. Thinking that something provocative is happening, Kenta tries talking to Karin, only to bring about a series of misunderstandings. After Karin begins avoiding Kenta, he becomes determined to set things straight between them. However, the moment he gets close to her, she has a massive nosebleed!

This is Karin's true secret—rather than sucking it out of humans, she periodically produces excessive amounts of blood, leading to nosebleeds if she does not release it. Unfortunately, her blood seems to react strangely to Kenta. Armed with knowledge of Karin's truth, will Kenta be able to keep her secret?