War has been running so long nobody remembers why it started, and that meaninglessness becomes the real enemy. Sara and her classmates pilot Strains not because they believe in Union or Deague, but because the machine is all they have. The show strips away the heroic veneer of mecha until you're watching children operate weapons systems in a conflict nobody can justify, and that's a harder story to watch than any explosion.

Humanity splits into two warring factions, the Union and the Deague, locked in a conflict so old nobody remembers how it started. The Union fights with manned mecha called Strain, while the Deague fields unmanned Tumoru units. Sara Werec, a sixteen-year-old student at Grapera Space Armed Soldier Academy, trains to become a Reasoner, a Strain pilot. Five years earlier her older brother Ralph was sent on a special mission to a front 130 light years away, and orphaned young, she longs to be reunited with him. Then Deague forces strike her world, and Ralph is among the raiders who carry off a mysterious girl sleeping in a capsule. Sara takes a Strain and chases him, only to be overpowered by her own brother, who kills the other students and destroys the academy. Left with nothing but questions, she returns to training under a new name, set on facing Ralph and understanding what he has done.