Zero Enna, alias Rei, is a 15-year-old cadet training to pilot humanoid weapons named Ingrids, engineered to defend humanity’s final bastion, Zion, against alien menaces dubbed Victim. Born on a remote colony, he lost his father young and was raised by his mother. A childhood Victim attack nearly claimed his life until a white Ingrid intervened, an event that fueled his resolve to become a pilot.

He joins the Goddess Operation Academy (G.O.A.), where rare EO blood type and latent EX ability—a superhuman link between pilot and Ingrid—are prerequisites. Designated Candidate 88, he forges a partnership with Kizna Towryk, a sharp-witted repairer charged with maintaining his Ingrid and curbing hazardous feedback during missions. Defying protocols, he achieves full synchronization with the Ingrid Eeva-Leena during an unsanctioned encounter, surviving lethal risks and branding him an anomaly among peers.

His appearance features spiky brown hair in the anime (contrasting the manga’s black), piercing blue eyes, and a compact 1.56-meter frame. EX reactions trigger a temporary shift to bluish hair. Outwardly, he exudes relentless cheerfulness and optimism, masking inner turmoil. Though physically adept, his bluntness and thickheadedness occasionally strain relationships. A paralyzing zero-gravity phobia complicates training, challenging his pilot aspirations.

His narrative arc remains open-ended. The anime concludes ambiguously, while a follow-up OVA extends the story without resolution. The opening animation teases his eventual success as a pilot, undepicted in released content. His EX ability, likened to “carbon not yet formed into a diamond,” lingers unmastered, symbolizing untapped potential.