OP⚔~Isekai~Reincarnation

the boy enters the most challenging online game, “Dungeon Attack,” where he becomes the first to unlock the achievement of defeating all the Demon Lords. After completing the game, he suddenly finds himself sent into the game world. He had been reincarnated as “Dantalian,” the lowest and weakest Demon Lord

when mc dreamt the same dream every night growing up where he would find himself in a different world, playing a game with mysterious unknown people, he looked forward to this escape from reality. That was until he found out the true nature of the nameless people and their motives.