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?