In a world where humans and demons coexist across Assiah and Gehenna, connected by possession, Satan, the ruler of Gehenna, seeks to invade Assiah by sending his son Rin Okumura. Unaware of his demonic lineage, Rin, initially an ordinary troublemaker, faces a turning point when attacked by demons. Learning he is Satan's offspring and a potential vessel, Rin rejects his fate and opts to train as an exorcist with his brother to protect Assiah instead.