In Flandore, the last human city-state sealed inside glass domes, nobility alone can awaken mana: the power that fights the monsters beyond the walls. Kufa Vampir, a half-vampire agent of the guild White Night, is sent to tutor the noble heir Melida Angel, who has shown no sign of mana at thirteen. His real orders are to quietly eliminate her if she turns out to be a fraud, but teaching her forces Kufa to question the assignment he was given.