The last remaining humans in Flandore are defenseless against the vicious monsters lurking outside their glass walls - relying solely on the Noble class's ability to wield mana magic. Melida, the heir to the House of Angel, has yet to exhibit her magical powers upon coming of age, prompting her grandfather to send half-vampire Kufa to intervene. He's given strict orders - if Melida is unable to manifest her mana, Kufa must execute her for having impure blood. Distraught by Melida's failure, Kufa can't bring himself to carry out such a cruel act against the spirited young woman, whose only sin was being born to an adulterous mother. Instead, he defies his orders, breaking the law by transferring a share of his own mana to Melida.