Akira Kamui, a middle school student descended from the Kamui family lineage, safeguards a legacy connected to mysterious Edo-period space capsules. His family endures severe poverty, driving him and younger brother Ai to steal a treasured heirloom map for financial relief. This act coincides with an alien invasion by the militaristic Zeno Palace, abruptly pulling Akira into an interstellar war.

Hot-blooded and impulsive, Akira frequently acts without forethought, fueling social struggles and unpopularity. When he, Ai, and classmate Kanna Uryu unearth the dormant giant mecha Tri-Zenon—one of three buried Zenon Guardians—they awaken it, becoming its core pilots. Akira serves as primary operator alongside Ai and Kanna, defending Earth.

Family dynamics shape his world: father Gontarou Kamui exhibits brute strength but often obstructs through foolishness; mother Reiko Kamui departed under ambiguous circumstances before the series. Ai balances Akira's rashness with sharp intellect, sharing their legacy and poverty. The loyal family dog Gon remains a constant companion. Kanna Uryu, as a fellow pilot, adds romantic tension to their battlefield partnership.

Piloting Tri-Zenon demands synchronization among Akira, Ai, and Kanna aboard the battleship Izumo during clashes with Zeno Palace. This role compels Akira to temper his recklessness, fostering teamwork and discipline throughout the conflict.