Kaito Minamoto, a reluctant teenager, never asked to be the last descendant of a legendary exorcist bloodline. But when a school trip to an ancient shrine accidentally leads him to break a sacred seal, he unleashes an Oni Lord-a demon his ancestors swore to destroy. With the help of his fiercely loyal best friend Aiko (a shrine maiden with secrets of her own) and the rogue exorcist Ryu, Kaito must master his dormant powers to prevent the Oni Lord from devouring the world. Their quest takes them to cursed mountains, forgotten temples, and into battles against yokai-supernatural creatures drawn to Kaito's awakening power. Along the way, Kaito learns the truth about his family's tragic past and the Blade of Raiden, a sacred sword tied to his destiny. But when Aiko reveals her half-oni heritage and sacrifices herself to save him, Kaito faces an impossible choice: accept her death or venture into the underworld to defy fate itself. Haunted by prophecies of a rising fox spirit and armed with a blade that burns with ancestral fire, Kaito races against time to reclaim Aiko's soul-even if it means confronting the darkest corners of his legacy.