Nozomanu Fushi no Boukensha

最高の神銀級冒険者を目指し早十年。おちこぼれ銅級冒険者のレントは、ソロで潜った《水月の迷宮》で《龍》と遭遇し、その圧倒的な力の前に為す術なく喰われ――そして、レントは“目覚めた”。なぜか最弱モンスター「スケルトン」の姿で……!?　死してもなお遙かなる神銀級を目指して、不死者レントの『冒険』がいま、始まりを告げる！

The protagonist was an eternal copper rank adventurer of the frontier area, Lent. With his bad luck, he meets a powerful monster inside of the labyrinth and is defeated, before turning into a bone man《Skeleton》.

Agonizing because he can’t go to town in his current condition, he recalls the existence of monster evolution, and, with a goal to gain a body with muscle, he goes to defeat the monsters of the labyrinth.