Naoto, once sentenced to death by his clan for his mother's crimes, was saved by his grandfather Masato Himura—also known as the legendary warrior Susano—who chose exile to protect him. Nine years later, Naoto lives in a world where humans, monsters, and mystical creatures coexist. Alongside his stepsister Mirai, he leads a mostly normal life as a high school student by day and a monster hunter by night—until a mysterious silver-haired knight appears and changes everything.