Ai Kamui is the younger brother of Akira Kamui, part of the Kamui family lineage charged with protecting Earth from the Zenon Empire invasion. An elementary school student noted for his high intelligence, Ai is frequently mistaken for a girl due to his feminine appearance. He, his brother Akira, and Kanna Uryuu become pilots of Tri-Zenon, a giant robot guardian discovered in a buried space capsule on the Kamui property. Tri-Zenon awakens to counter galactic invaders searching for three hidden Zenon artifacts.

His family includes their physically strong but often hindering father, Gontarou Kamui, and their mother, Reiko Kamui, who left the household for undisclosed reasons before the story's events. The family dog, Gon, is a loyal companion. Ai pilots Tri-Zenon as part of a collective defense alongside other awakened units—Gaia-Zenon and Alma-Zenon—and their pilots.