Rei Kazama was part of Kei Munakata's éX-Driver team before Lisa Sakakino and Lorna Endō joined, serving alongside individuals like Joe Todo, who later turned adversary over disagreements on the limits of éX-Driver duties.

After this team period, Rei became a licensed freelance agent intercepting rogue AI vehicles, a role requiring an extra certification granted only for exceptional driving skill, situational judgment, and composure. Operating under the designation éX-Rider, she favored a powerful motorcycle for its superior mobility, personally maintaining it with advanced mechanical skills and refusing others, including team mechanic Ogawa, from performing repairs or modifications.

Her personality exhibits pronounced self-confidence, reflected in provocative dress and forthright behavior, yet she remains typically calm and friendly compared to more volatile individuals like Lisa. Her competence and attitude significantly impacted Souichi Sugano, who developed notable admiration for her.

Within the "éX-Driver: Danger Zone" narrative set before the main series, Rei partners with Nina Anna Thunder. Nina acts as primary driver of a highly modified white Roadster replica, while Rei serves as co-driver and systems operator, managing the car's advanced technology including supercharger, turbo, and nitrous injection systems during missions to stop rogue AI vehicles. Their partnership confronts a specific incident involving a malfunctioning miniature AI car and the related conspiracy, dealing with both the immediate threat and troubles within the éX-Driver organization itself.