Tsukasa, a college student, is rescued from an attack by a devil, one of many vampires that can blend in among the human population. Anzai, her savior, is a half-devil who exploits his supernatural gifts as a member of a shadowy police task force that specializes in devil-related crime in Tokyo.

As Anzai continues to keep guard over Tsukasa, the two quickly forge a tentative bondone that Anzai fears will test his iron-clad rule of never drinking human blood…