In 2025 AD, after a sudden invasion of intergalactic kaiju, a painfully shy boy, Tetsuo Yabusame, saves the autonomous bomb Yukio and becomes an unlikely defender of Earth. Ten years later, now hailed as a "savior", Tetsuo heads into space with Yukio for the Final Battle. With 20,000 kaiju closing in, humanity's fate is on the line to bring an end to this relentless conflict!

Tetsuo is gradually accepted by Ao and the others he meets on the frozen Earth. However, his peace is short-lived, as he is attacked by a galactic monster unlike any he has ever fought before. As people flee in unison, Tetsuo stands alone against the monster. He finds himself in a desperate situation against its overwhelming power, but just when all hope seems lost, who should appear—!