Nozomanu Fushi no Boukensha

Nozomanu Fushi no Boukensha follows Rentt Faina, a veteran adventurer who has spent years scraping by without ever rising far in the ranks. During a routine expedition into a labyrinth, he stumbles upon a dragon's lair and is killed on the spot. He awakens to a horrifying new existence as a skeleton, the lowest class of undead monster, and is forced to fight his way through the labyrinth while hiding what he has become. As Rentt discovers that defeating other monsters grants him experience and pushes him toward higher stages of undead evolution, he sets his sights on a nearly impossible goal: becoming a vampire, the highest form of undead and one close enough to human life that he might reclaim some normalcy. Forced to conceal both his past identity and his monstrous nature beneath an unremovable mask, he eventually returns to society with help from Lorraine Vivier, an elite researcher and retired adventurer. Taking Lorraine's surname, Rentt starts again as a rookie while still chasing his childhood dream of reaching mithril-class status. Every step forward now demands caution, because the adventurers' guild would not hesitate to exterminate the monster hidden behind his human face.