Gunmen are... they're the machines the beastmen used to kill any humans who ventured to the surface. Gunmen are sort of like robots, but they're very large and they can be piloted by a single beastmen. Their energy and willpower drive the gunmen, but they also have to maneuver it with controls. It's the most advanced technology I've seen, but they're surprisingly easy to pilot once you get the hang of it.