The blood-slick floor of the Demon Lord's throne room still reflects the faces of the allies who betrayed him. Baek Mu-Gun was not a tyrant. He was a reformer, a heretic against the orthodox sects, a Heavenly Demon who believed the murim could be healed instead of ruled. For that, the Alliance sealed his soul inside a jar and cast him into the abyss. A century later, something cracks the jar open. He wakes not in the demonic palace but in a novice's dormitory. The body he wears belongs to Baek Mu-Sang, the youngest disciple of the Venerable Sect of the Sword — the weakest student in the weakest hall, a boy so talentless the instructors call him a waste of incense.

The martial world he returns to has forgotten him. The Alliance he once challenged now rules unchallenged. The demonic cult he founded has been erased from history. And Mu-Gun, trapped in a body that cannot perform a single proper technique, must begin again from the bottom. He applies the breathing methods of the Heavenly Demon to the orthodox curriculum of the Venerable Sect and discovers a synergy no one in a hundred years has been alive to see. The boy who could not swing a sword is about to dismantle every hierarchy the murim holds sacred — but the Alliance has not forgotten the scent of old heresy, and somewhere in the shadows, someone has noticed that the jar is empty.

Also known as: Heavenly Demon Reborn, 천마는 환생한다, Cheonmaneun Hwansaenghanda, Heavenly Demon Reincarnation.