The Legend of the Shining Sword

Eunho, the strongest being in the spirit realm, descended into an empty life of relentless slaughter when he tragically lost the mortal woman he loved. Seeking redemption and a chance to live as a human, he repents for a thousand years and willingly sacrifices the core of his power in order to be reincarnated. But when he is finally reborn, he’s shocked to find himself in the body of a frail young boy. Now, the former king must navigate his new life as a powerless human and master martial arts, the very practice mortals once used against him.

Source: Tappytoon