Nozomanu Fushi no Boukensha

Lento Feyner has been stuck as a bronze rank adventurer for 10 years, but while exploring the labyrinth he accidentally discovers a dragon and is killed. However, he finds himself still conscious in the body of a skeleton, and resolves to kill monsters to take their magical power in the hopes that he will be able to evolve as a monster and obtain a human-like body one day.