Rentt Faina, a seasoned but mediocre adventurer, meets his end when he faces a dragon inside a labyrinth. To his surprise, he comes back to life as a skeleton, one of the weakest forms of undead. Rentt learns that by defeating other creatures in the labyrinth, he can gain experience and advance through different undead stages, eventually reaching forms with restored flesh. Driven by this discovery, he resolves to keep evolving, with his ultimate aim being to attain the highest level of undead—a vampire, which looks nearly human.
Concealing his past and current monstrous appearance with an unremovable mask, Rentt tries to rebuild his life. He is taken in by Lorraine Vivier, a renowned former adventurer and top-tier researcher, who lets him use her name and start over as a beginner. As he works toward his childhood dream of becoming a mithril-class adventurer, Rentt must be careful not to reveal his true nature, knowing that the adventurer's guild might see him as a threat and destroy him.
