The Unwanted Immortal Adventurer is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.nl fastest updating comic site. The Summary is

The protagonist was an eternal copper rank adventurer of frontier area, Lent. He’s unlucky as he meet a powerful monster inside of the labyrinth, got defeated, and when he noticed, he already became a bone man《Skeleton》. Agonizing since he can’t enter the town with his current condition, he’s recalling about the existence of monster evolution, with a goal to gain a body with muscle, he defeats the monsters of the labyrinth.