Cast: Okano Yuu

It details the life of a mid-rank soldier who died at the very end of the war against the Demon Race. Fortunately for him, he wakes up to find that he’s a baby again, in the embrace of his real mother, years in the past. Determined to avoid the chain of tragedies that took his beloved ones away from him, he takes advantage of the advancements in swordsmanship and magic that developed during the war (as we all know, wars are when many scientific breakthroughs tend to happen), and tries his best to prepare for the demon invasion as well as strengthen himself with maximum efficiency. Description taken from Hot Chocolate Scans. 

The protagonist was an eternal copper rank adventurer of frontier area named 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.

After a long-standing battle between the demons and humanity, the Demon King Luruslia Nord was laid to rest at the hands of a hero. However, his soul continued to wander. After thousands of years, Luru awakened in a world devoid of demons. Moreover, he was reincarnated as a weak human! To search for his disappeared brethren and to understand the meaning of the new "life" he's been granted, Luru sets forth on a new adventure.