Jun Kazami is a young mechanic working at a small tuning shop called Mechadoc in eastern Japan. When he discovers a beaten-down Toyota Celica XX in a junkyard, he sees not just a broken car but a chance to prove his skills. With help from his friends, including the shop's finance manager Ichiro Nakamura and fellow tuner Kiyoshi Noro, Jun rebuilds the Celica, modifying it with custom parts, twin turbos, and nitrous oxide to transform a regular street car into a genuine racing machine. His goal is to compete against and surpass his rivals, most notably Nachi Wataru, a tuner and racer who drives a Mazda RX-7, and the legendary Watanabe Toshimitsu, known as the best racer in Japan, who pilots a Nissan Fairlady Z.

The story follows Jun and the Mechadoc crew as they engage in various forms of motorsport against a colorful cast of opponents. One major narrative arc involves a cross-country endurance race inspired by the Cannonball Run, where the team must test not just their car's performance but their endurance and strategy over a long distance. Other storylines focus on different racing disciplines, including drag races called zero-yon, where the team later fields a mid-engined Honda CR-X, and circuit battles with a Nissan Fairlady Z. The tuning shop rivalry deepens as Jun faces off against competitors from other garages, including Champ, a rival shop whose driver uses an RX-7. Beyond the main competitors, the manga features appearances from classic Japanese cars, including the Nissan Skyline GT-R, the Toyota 2000GT, and even comic relief from a group of bosozoku driving an old Toyota Celica. The series is notable for its authentic depiction of car parts and real engine sounds, with races won through mechanical skill and tuning knowledge rather than gimmicks, reflecting the manga's celebration of automotive culture and the dream of building a superior machine from the ground up.