In an era when the boundary between the mortal and supernatural realms has grown dangerously thin, demons steal ten sacred artifacts known as the Jingi or Sacred Relics from the human imperial capital. The emperor issues a decree to all onmyoji who serve the empire: recover the treasures at any cost. Among them is Fuzuki, a brilliant renegade known as the Heretic, feared for his occult practices and a technique that uses his own blood. He is joined by Hakuro, a loyal swordsman with canine animal features who easily wields a long sword. While searching for the first Relic, Fuzuki encounters Ranmaru, a young half-demon, half-human boy who has been rejected by everyone around him and who stands at the center of the growing chaos.

The companions secure the first two Sacred Relics before being summoned to the imperial court. There, they are plunged into political scheming and a cutthroat fight for possession of the Relics, leading to the intervention of the emperor himself, which reveals hidden bonds between the sovereign and the heretic onmyoji. During a mission to investigate the unsettling disappearances of young women near Mount Goun, Hakuro is sidelined by injuries, forcing Fuzuki to head off with Ranmaru. They are directed to a supposedly abandoned manor deep in the mountains, where they come face to face with a deadly demon that proves impervious to Fuzuki’s attacks.

The narrative explores Fuzuki’s past through his fractured relationship with Toyochika. The two met as children when Toyochika was an onmyoji in training and Fuzuki was the crown prince he was sworn to protect. A serious, horrific incident caused their paths to diverge, and now Toyochika harbors an unyielding anger toward his former liege. However, the deep bonds of the past are not easily severed, and the two onmyoji must work closely together again in the fight against the demons of the Basara Clan. As the search for the remaining Relics continues, the half-demon boy Ranmaru carries a Jingi within his head, making his destiny central to the conflict that threatens to overturn both the human and demon realms.