World Destruction: Sekai Bokumetsu no Rokunin

The timid Simon and the brash Kamina led a relatively uneventful life in their underground cave community, until one day Simon found something that would change their lives forever: what seemed like a large face in the wall. But before he could show off his discovery, their cave was assaulted by a strange giant robot; even more strange was the red-haired, gun-toting vixen who swooped in simultaneously to join the battle. The battle isn't going their way, however, until the three think of the best way to kill a giant robot: another giant robot. Soon they find themselves inside the object that Simon found — a robot known as a Ganmen — and blast their way to the harsh surface of the planet. Now, as the three meet new friends and figure out how to use their new method of transportation, they set out to navigate the planet and investigate the source of the giant robots and their "Beastmen" pilots.