In a modern Japan where vampires, called devils, live hidden among ordinary people, Yuuki Anzai works for the Metropolitan Police Department's Public Safety Division 5, cracking down on devil-related crime. A half-devil himself, he meets graduate student Tsukasa Taira during an investigation into a string of vampire killings. As the two grow close, Anzai struggles to keep his own bloodlust in check while the case pulls them toward an organization with its own designs on devils.