Kyouko Mejiro is a private detective who befriended Nazuna Nanakusa in high school, eventually discovering her true heritage as a vampire. On her eighteenth birthday, Kyouko's father, who had been transformed into a vampire, had murdered her mother and attacked her, so Kyouko was forced to kill him in self-defense. Her family tragedy drove her to despise vampires, setting out to become a highly skilled detective, under the alias Anko Uguisu.