Mangnani Sogyojuro Hwansaenghaetda

Once a rising martial arts master, Ja-Gak Yang is known as the Ten Strike Finisher due to his ability to defeat any opponent within ten moves. Ja-Gak is also the son of the leader of the Great Martial Alliance, an organization of virtuous martial arts sects. His future leadership over the martial arts world seems all but assured -- that is, until he is assassinated by jealous rivals! Ja-Gak is reincarnated into the body of Cheon-So Ma, the playboy second-in-command of the evil Shining Light Cult. Can Ja-Gak remain true to his principles despite his new life on the dark side?

(Source: WEBTOON, edited)