The hero Alexander leads a daring raid on the Demon King's castle, hoping to assassinate the ruler of the demonic kingdom and end a brutal war in one fell swoop. The assault ends in catastrophe, as Alexander and his comrades are effortlessly slaughtered by the Demon King's overwhelming power. Yet death does not mark the end of Alexander's journey. He awakens two years later, reincarnated as Zilbagias, the seventh prince of the very demon king who killed him. Retaining the memories and will of his past life, the reborn hero vows to use this miraculous second chance to destroy the demonic kingdom from within, tearing it apart as a false prince of the enemy he swore to vanquish.

The story follows Zilbagias as he navigates the treacherous political landscape of the demonic realm. In a short span of five years, he distinguishes himself as a prodigy, forming a forbidden contract with the Devil God of Taboo and acquiring a high elf pet, which grants him access to healing miracles unheard of among demons. These unnatural talents make it difficult to maintain his disguise, but they also provide the tools he needs to rise through the ranks. His first major test comes when he confronts Faravugi, the White Dragon chief who was his comrade in his previous life. After defeating this former ally, he takes Faravugis daughter, Layla, as his companion. This act forces Zilbagias to partially reveal his plans to her, forging a complicated relationship built on shared secrets and a mutual desire for destruction.

As his first deployment to the front lines of the war against the Panhuman Alliance approaches, Zilbagias is sent to the territory of the Rage family to prepare his assault. He later returns to the village of the Reiju tribe to recruit soldiers, only to witness the horrifying reality of humans who are raised like livestock on farms. His training for the coming battle culminates in a brutal killing match against captured heroes, an act that forces him to confront the moral weight of slaughtering his own people while maintaining his cover. Throughout these trials, Zilbagias begins weaving fragile alliances with powerful figures in the demonic kingdom, including the lich Enma, all while secretly planning their inevitable betrayal. Set in a dark fantasy world where humans are oppressed and demons reign through brutal hierarchies, Zilbagias wages a lonely war of vengeance, burning with the flames of retribution as he walks the tightrope between his human heart and his monstrous identity.