From Bandai Entertainment:
In his skyless cavern of a village Simon toils daily, drilling holes to expand his stifling little world until one day he makes an extraordinary discovery: a small glowing drill bit and the man-sized mech it activates. Before he can give it a second thought Simon's dragged into a plot to break through to the surface by the local gang leader Kamina, only to have the ceiling come crashing down on top of them under the weight of a giant monster! It somehow falls onto the boisterous Kamina and cowardly Simon to defend their village, but once they defeat the monster what awaits the duo on the surface world? Get ready for buxom babes, beastmen, and giant mechs as only GAINAX can provide them.