Yuji Sano was a normal guy working a soul-sucking nine-to-five job when he suddenly found himself transported to a fantasy world where he restarted his life as a Monster Tamer. After befriending the Slimes, Yuji is quickly able to gain a second character class, ranking up his stats and learning new skills as he encounters one surprise after another.

Yuji decides that the best way to crush the Laboratory, an evil organization with a murderous track record, is to go undercover. After revealing he has read the Magic Book of Etwas, the organization welcomes him in with open arms. However, trouble soon arises when Yuji, required to register his magic power as part of the onboarding process, shorts the device used to measure it. The more he tries to stay incognito, the more he stands out!