Manga D Genesis: Dungeon ga Dekite 3-nen

It has been 3 years since the first dungeon, a giant cave filled with monsters, was born. In a world where dungeon raiders are common, Yoshimura, who lives his life as company livestock, unexpectedly (and unfortunately?) ranks first in the world rankings! Wishing for a more laidback lifestyle, he retires and decides to enter the dungeon. Wielding unknown skills that he has gotten, he joins the the frontline of the dungeon raiders. What will be the future of his laidback life?