Tsukasa Taira, a college student in Tokyo, is pulled out of a night attack by Yuuki Anzai, an officer of the police's Division 5, which handles crimes committed by devils, the blood-drinking beings who live hidden among humans. Anzai is half devil himself, and the rule he has kept his whole life, never to taste human blood, starts to give the closer he gets to Tsukasa: anger, fear or desire is enough to tip him. Tensions between the two species keep rising around them.