Failed Bronze-class adventurer Rento has spent the last ten years striving to attain the rank of Mythril adventurer. When he journeys alone into the “Watermoon Labyrinth”, he encounters a dragon, and, helpless before its vast power, is eaten. ―― Then he wakes up. For some reason, though, it‘s in the form ofa skeleton, the weakest monster of them all! To avoid being slain by monsters and adventurers, Rento decides to use the power of “existence evolution”, defeating othergaining experience, allowing him to evolve into a more powerful monster. ​

If he can evolve into a “ghoul”, he might be able to fool people into thinking he’s human. And then, he meets the human rookie adventurer, Rina Lupage. When he saves her from monsters, he realizes how strong his new power is…! As he battles powerful monsters, he encounters many mysteries and gets stronger. ​

Even in death, the undead Rento still strives to become a Mythril-class adventurer!