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.

Every single member of The Laboratory was sacrificed in order to give birth to a dragon. Could this dragon be the fabled Dragon of Dark Ruin, destined to destroy the world?! Yuji finds himself in a stalemate against the fearsome foe when the Slimes make a useful discovery! Has Yuji finally met his match or will he save the world?!