Fukafuka Dungeon Kouryakuki: Ore no Isekai Tensei Boukentan

There is one place that has withstood attempts by every army to conquer it—the city-sized labyrinth known as the Deepest, Most Unknowable Dungeon. But now, after dying on Earth as a young temp worker, Jean is reborn into the world with a fascination for its most infamous dungeon. With the right training and the most carefully chosen set of lustful comrades-in-arms, he may have the chance to accomplish the impossible and become a legend in a new fantasy world!

(Source: Seven Seas Entertainment)