A salaryman meets an untimely demise and gets reincarnated in a fantasy world as a fifteen-year-old boy named Luciel. Luciel uses his business skills to talk his way into a nearby town's Healers' Guild, where he begins a crash course in magic.

Luciel starts to get a handle on his healing powers and what it's going to take to improve them and survive in this new world, so he charts a course for a rather unexpected training destination—the Adventurers' Guild!

Luciel registers with the Adventurers' Guild and begins martial arts training with chief instructor Brod. As part of that training, he is forced to drink Substance X, a mysterious and disgusting beverage that confers special powers like a cheat item.

Luciel gets a break from training to learn about butchering monsters with Gulgar's brother, Galba, and study world history and culture with Nanaella. While shopping with Nanaella one day, he discovers Monika unconscious and bleeding on the street.

It's been a year and Luciel needs to renew his registration at the Healer's Guild. What rank will he be? Luciel jumps into the next level of his training, when he encounters the Healer who left Monika to die...

After Luciel's encounter with Bottaculli, Brod decides that he'll need to get even stronger to survive whatever the corrupt healer might throw at him. Little do they expect the mysterious letter that's about to arrive and change everything.

Luciel makes his intrepid, if reluctant, trip the Holy City of Shurule, where he learns more about the Church and what he'll be doing there. Is this a setup? Or just another stepping stone on the path to survival?

Luciel makes progress at his new job, potentially even getting in over his head. He's up against a strange encounter in the boss room, and an even more mysterious one afterward...

Luciel starts to doubt his fighting skills after clearing the boss room on the tenth level, so he asks to train with Lumina and the Valkyrie Paladin Regiment. After clearing the twentieth level, he meets the pope again to learn more about the wights.

Luciel agrees to heal the adventurers in Shurule but demands that they stop calling him "maso-zombie." Cattleya realizes Luciel has been consuming Substance X and informs the pope, who explains the origin of the mysterious drink.

The depths of the undead labyrinth force Luciel to keep going, testing his mettle as a healer and an adventurer. What will he find at the end, and what will he find when he finally returns to the surface?