Ore to Kimitachi no Dungeon Sensou @COMIC

In the year 2045, Earth has been invaded from four different worlds. To defend itself, Earth must conquer the dungeons that connect to the other worlds. Each nation selects a "delver" to take on that duty, and Japan chooses Gunma, an ordinary guy who suddenly finds himself dispatched to the front lines! Heavily armed and terrified, and activating...