A girl who built robots as escapism suddenly has to pilot one while the world collapses around her. The show doesn't pretend this is heroic. It's watching someone realize that her hobby became her only skill, and now that skill is the only thing keeping people alive. What starts as a straightforward mecha action series pivots hard into something quieter and meaner, where every victory costs someone something irreplaceable, and Aoba has to keep moving anyway because stopping means everyone dies.

Aoba is a lonely teenage girl who loves assembling plastic model robots and lives alone with her grandmother until the older woman dies. Soon afterward, her own mother takes her by force to a secret base in the South American jungle, run by an organization called Angel. There, piloted giant robots such as Moribito Number 2 fight the Ancient-Jinki, enemies that rose from below the ground, out in the Grand Savanna. The real purpose behind these battles is kept hidden. Aoba works hard at the base, hoping to one day pilot a robot herself and uncover those secrets, while a bigger danger gathers out of sight.