Dungeon Wars with You and Me

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 his "listening carefully" and "enemy detection" skills, he encounters the world's strongest beauty. "Shall we shower ourselves with blood together?" "Strategic retreat, plz!" She's wicked strong but has tofu for brains, and they advance through the dungeon with unstoppable momentum...? An untrodden dungeon fantasy where everything gets mowed down with ease! (Source: TO Books, translated)