Kazami Jun stands as the narrative's central figure, embodying dual roles as both tuner and racer. At 18 years old, he runs the small tuning shop "Mechadoc" alongside teammates Ichiro Nakamura and Kiyoshi Noro. His driving ambition centers on outperforming rivals like Nachi Wataru and the legendary Fairlady Z driver Watanabe Toshimitsu in racing competitions.

Jun specializes in transforming ordinary, non-racing vehicles into competitive machines that challenge purpose-built racing cars. His technical skill shines through authentic depictions of mechanical components during these conversions. Key examples include his work on the CELICA XX 2800GT, CR-X Mid, and Gracer Z Z31 300ZX.

Throughout the series, Jun enters diverse races and vehicular challenges, confronting established racers to prove Mechadoc’s tuning prowess. These events showcase his technical abilities while elevating his standing in racing circles. Episodes such as "Take the Glorious Finish Line" and "Conclusion! The Circuit Grand Prix" mark critical milestones in his racing journey.

Professional tensions surface within Mechadoc’s team dynamics, highlighted by the episode "Mecha-Doc Breaks Up!", signaling organizational strife impacting Jun’s world. Subsequent episodes like "The Tokyo-Nagoya Circuit Sprint!" and "Flooring the Gas Pedal of Youth!" track his ongoing career progression and personal maturation.

Jun’s relationships extend beyond rivalries to collaborations. Ichiro Nakamura handles shop finances despite minimal mechanical expertise, while Kiyoshi Noro provides technical support. The team also interacts with figures like Reiko Ono (Sukebo Komachi), whose SPORTS800 and 2000GT MF10 vehicles undergo specialized tuning at Mechadoc.