Sara Ishida, freshly graduated from Tokyo’s elite Shinbudai officer academy, commands the 108th Guard Division’s 4th Company—a remote Aomori outpost dubbed a "reject camp" for misfit pilots. Her rigid adherence to protocol clashes with the unruly unit’s defiance, complicating her dual mandate to repel Phantom Beast invasions and forge discipline in untested soldiers. When their first combat deployment collapses into chaos as panicked subordinates ignore orders, the failure forces Sara to confront her overreliance on authority alone.

Amid escalating alien threats, she recalibrates her leadership, analyzing her team’s inexperience and frayed morale. Gradually, she shifts tactics to cultivate trust and coordination within the ranks while overseeing aging Humanoid Walking Tanks (HWTs)—single-seat eikougou and two-seat koukigou models—that serve as the unit’s last line of defense. Military brass scrutinize her every setback, yet Sara persists, balancing tactical adjustments with the 108th’s operational constraints.

A trench coat-clad penguin dubbed Hard-Boiled Penguin, voiced by Norio Wakamoto, intermittently surfaces with cryptic observations unrelated to Sara’s command struggles. Her past remains undefined beyond her service record, with narrative focus fixed on her tactical evolution amid Aomori’s sudden Phantom Beast onslaught—a crisis that exposes the division’s marginalization. Through repeated clashes, Sara navigates setbacks and incremental breakthroughs, her journey reflecting the grind of transforming outcasts into soldiers without sacrificing strategic rigor.