Life of a Demon Hunter

After 12 years of horrible nightmares that prevent him from getting sleep, Ujin Kim dies and wakes up to find himself in the world from his nightmares! Surrounded by demons of all kinds, he quickly realizes that he's been reincarnated into the body of a mercenary and heads out to find civilization. He quickly learns that this is a world filled with magic, a Church fighting the demons, and all sorts of sketchy characters. But hey, at least he's finally able to get some sleep!

(Source: Webtoon Entertainment)