The Right Arm of the Saint I.Kojo Akatsuki, a high school student living on Itogami Island, is suspected of being a powerful vampire called the Fourth Progenitor. On his way home, he notices a female student trailing him. After an altercation with two local demons, he learns that Yukina Himeragi is an 'attack mage' (攻魔師, koumashi) sent by a secret organization to observe him and the two begin to spend time together.