Post-war Japan is split into four military zones, each controlled by rival nations vying for total dominance. Although the Boundary War, fought using humanoid mecha known as AMAIM, has long ended, the conflict between these factions persists, leaving the Japanese population under heavy oppression. Amou Shiiba, a 16-year-old orphan secretly restoring an abandoned AMAIM called Kenbu, encounters Gai, an autonomous AI requiring battery power. By deciding to assist each other, Amou and Gai become central to a catastrophe, resulting in Amou being branded a terrorist and ostracized by society. Nevertheless, Amou refuses to stand by in the face of injustice and sets off on a lengthy journey filled with hardship and companionship. His goal shifts from seeking a quiet life to freeing the Japanese people.