I Reincarnated As The Crazed Heir

Once a rising martial arts master, Jagak Yang is known as the Ten Strike Finisher due to his ability to defeat any opponent within ten moves. Jagak 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! Jagak is reincarnated into the body of Cheonso Ma, the playboy second-in-command of the evil Shining Light Cult. Can Jagak remain true to his principles despite his new life on the dark side?
Yang Jagak, who was assassinated through poison during the political wars of the Murim. While he thought he was dead, he realized he was in the body of another person.He found out that he is in the Demon Cult, the art he knows is the Heavenly Demon God Arts, and the owner of the body was the crazed heir who lusted after women.Why did it need to be the Demon Cult, and why did it need to be this person?