Murim Song Gongmuwoneuro Saraganeun Beop

One day, Yeon Woo-Hyeok fell into the world of martial arts and became a civil servant in the martial arts world.

Yeon Woo-Hyeok, a veteran of the martial arts mystery game [The Great Revolutionary King's Great Pokai], one day finds himself possessed by a Po-Kwai in the game without warning. Fortunately, he realizes that the events in the game that he had memorized are exactly as they appear, and begins to adapt to being a Po-Kwai in the game while solving the cases. However, the joy is short-lived as Yeon Woo-Hyeok's ability, 'Young-An', is actually an upper chamber opening, and because of this, he is in danger of dying. No, being a Po-Kwai is difficult, so he has to learn martial arts to become a powerful master?!

(Source: KakaoPage, translated)