The fourth primogenitor is the most powerful vampire once thought to exist only in the world of legends. Yet when it appears in Japan, the government for some reason chooses an apprentice “sward shaman“, Yukina Himeragi, to observe and obliterate it. Bewildered by the disproportionate task and its specific details, Yukina arrives at the Demon District of Itogami-jima to watch Akatsuki Kojo, and a student at a private high school on Itogami-jima.