Maaka Karin hails from a line of vampires in Japan, but she is far from a typical one. While most vampires consume the blood of others, Karin’s body overproduces blood, forcing her to dispose of the excess by feeding it to her “victims” once a month. Despite this, she manages to attend school like any other girl her age. The situation becomes more complicated when a new transfer student, Usui Kenta, joins her class. Karin’s blood production surges in his presence, almost as if he triggers it. Unfortunately, Kenta soon discovers Karin’s true nature.