The story takes place in an alternate reality where the existence of demons has long been acknowledged; there is even an island in the Pacific Ocean called "Itogamidzima," where demons are full citizens and enjoy equal rights with humans. However, there are also mage-people who hunt them, especially vampires. An ordinary Japanese schoolboy named Akatsuki Kojyo inexplicably turned into a "pure‑blood vampire," the fourth of its kind. A young woman, Himeraqi Yukina—known as the "blade shaman"—begins to follow him; she must keep an eye on Akatsuki and kill him if he goes out of control.