Reverse vampire Karin Maaka can't help it: classmate and coworker Kenta Usui's unhappiness triggers her bloodlust. Although she's learned to control her urges around Kenta, when her excess blood becomes too much to handle, even Kenta isn't safe! When upperclassman Ayaha Ougimachi appears on the scene, things become all the stranger. Meanwhile, the bossy, overbearing Ayaha incites Karin's bloodlust, so much so that Karin bites the girl! When Ayaha becomes increasingly positive as a result of the blood injection, Karin's worries become deeper...