Three kids pilot a robot made of material nobody understands, living in a shelter where their real memories were stolen. The show never wastes an episode, building them as actual people before asking them to save what's left of humanity. The mecha designs look awkward on purpose, like teenagers jury-rigging salvation from broken world scraps.
Humanity clings to survival in underground shelters after an alien invasion decimates the world above. The authorities keep the remaining population docile through strict control and enforced amnesia, erasing memories of the catastrophe that nearly ended civilization. Three ordinary teenagers discover they've been selected for a classified program: they're to become pilots of experimental combat machines forged from an otherworldly metal called Megatonium. When synchronized, their three mechas merge into a single colossal warrior named Musashi, humanity's last line of defense against threats lurking beyond the shelter walls. The series balances the weight of this impossible responsibility against the mundane reality of teenage existence. Between school routines and social pressures, these young pilots must master their machines and confront the truth about what really happened to the world. As they train for battles they don't fully understand, questions emerge about the shelter's leadership, the real nature of the invasion, and whether they're being prepared to save humanity or become pawns in a larger conspiracy. Their journey becomes one of uncovering hidden history while standing against forces that want those secrets buried forever.