After a tragic meeting, Kojou Akatsuki's days as an average high school student in Itogami Island's Demon District come to a sudden end, leaving him with the amazing talents of a vampire. It's not long until he's thrown into the spotlight when it's revealed that he's the fourth primogenitor, an incredibly strong vampire that most people dismiss as a legend. Fearing Kojou's destructive potential, the Lion King Organization sends in Yukina Himeragi, an apprentice sword-shaman, to keep an eye on him and, if he becomes a problem, to murder the world's most powerful vampire. As Kojou comes to grips with his skills as they both battle to defend the world, the two are forced together by fate and create an odd partnership.