Kojou Akatsuki's life as a typical high school student on Itogami Island is upended when he gains extraordinary vampire powers after a pivotal encounter. Soon, he learns he is the legendary Fourth Primogenitor, a vampire of immense strength that many deem a myth. The Lion King Organization, alarmed by his potential for destruction, dispatches Yukina Himeragi, a skilled apprentice sword-shaman, to keep him in check and eliminate him if necessary. As they navigate their tumultuous relationship, the duo must confront chaotic threats to the city while Kojou grapples with his newfound identity.