In contrast to her family, Karin Maaka is a vampire who walks in daylight and sleeps at night. No one in her town knows her true identity—and she intends to keep it that way, as it could jeopardize her "normal" life if someone were to find out. Kenta Usui witnesses Karin biting someone on the day he transfers into her class as a new student. Assuming something provocative is happening, Kenta tries talking to Karin, only to trigger 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 suffers a massive nosebleed! This is Karin's true secret—rather than sucking blood from humans, she periodically produces excessive amounts of it, 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?