Maaka Karin comes from a family of vampires living in Japan, but she is not a normal vampire. Vampires are normally supposed to drink the blood of their victims but Karin suffers from a condition that causes her body to produce excessive amounts of blood. About once a month, she has to get rid of the excess blood by giving it to her "victims." But she somehow manages to go to school like everyone else her age.<br><br>
Well, things are about to get more complicated. When a new student, Usui Kenta transfers into Karin's class, she starts producing unusually huge amounts of blood, almost as if in reaction to him. Worse, he happens upon Karin's true nature...