Kazuma, a 15-year-old resident of the lunar colony Eden in 2267, stands 175 cm tall. He is Takeru's best friend and serves as his foil, exhibiting a quiet, cool demeanor that contrasts with Takeru's impulsiveness. He has a younger sister named Chiyo. Initially, Kazuma competes with Takeru in tube races using specialized hovercraft-like vehicles. After Takeru discovers a photograph suggesting Earth may be habitable, Kazuma aids him in investigating Eden's suppressed secrets. They commandeer a moon rover to verify Earth's recovery, evading pursuing authorities and confirming Earth's habitability. Kazuma remains on the moon when Takeru and their friend Biz escape to Earth aboard a repurposed rocket. Stranded in Eden, Kazuma infiltrates the ruling council, ascending to a high-ranking security position. While outwardly loyal, he operates as a double agent, secretly sabotaging the council's control. Years later, when Takeru returns, Kazuma is ordered to capture him, sparking a physical confrontation fueled by Takeru's mistrust and Kazuma's hidden allegiance. Kazuma reveals his true loyalties by undermining the council and enabling the theft of the "Freedom" spacecraft—concealed Mars-colonization vessels—to facilitate mass migration to Earth. Kazuma's efforts assist the resistance in toppling Eden's authoritarian regime. He reconciles with Takeru and joins the exodus to Earth, transitioning from compliant citizen to architect of societal revolution.