Earth's Saviour is the Heavenly Demon

Our hero, regressed into his past self from a distant future of an apocalyptic earth of dungeons and monsters and constellations, after being betrayed by his freinds, his family, his teammates and the constellation. Essentially his entire life had been nothing but a game of betrayals. Yet, the moment he returned to his past self was when he was frail and weak, to the weakest point of his life, which essentially caused him to die.

Enters the Demon Lord of another world. What was destined to be a dead rotting body was now granted life by a transmigrated soul of a murim demon lord from another world.

This demon lord now inherits both the memories of the betrayal as well as the future knowledge of his self.

"Now watch as I bring mayhem on this world and to those who betrayed me, as it undergoes cataclysm"