Set in a near-future Japan, "AMAIM Warrior at the Borderline" depicts a nation divided and occupied by foreign powers following a global conflict. The story centers on Amou Shiiba, a young mechanic living in this fractured world. After losing his family in the war, Shiiba becomes entangled in a resistance movement when he discovers AMAIM, a highly advanced humanoid weapon. These machines, known as Kenbu, are piloted by individuals to combat the oppressive forces controlling Japan.

Shiiba forms a bond with Gai, an autonomous AI unit that assists him in piloting the AMAIM. Together, they join forces with the resistance group "Jissoji," which aims to reclaim Japan's sovereignty. The group includes characters like Kyosuke Yamanouchi, a skilled pilot and leader, and Risa Yukishiro, a determined fighter with her own motivations. As the resistance grows, Shiiba and his allies engage in battles against the occupying forces, utilizing their Kenbu to challenge the technologically superior enemy.

The narrative explores themes of resilience, identity, and the cost of freedom, as Shiiba grapples with his role in the conflict and his desire to protect what remains of his homeland. The series balances intense mecha battles with character-driven moments, highlighting the personal struggles and growth of its protagonists. Through its depiction of a divided Japan and the fight for liberation, "AMAIM Warrior at the Borderline" presents a story of hope and determination in the face of overwhelming adversity.