J is initially introduced as a battle racer serving in the Ogami Corps, having been trained under the wing of the antagonistic Dr. Ogami. His early approach to racing is defined by the ruthless, anything-to-win philosophy instilled in him by his mentor. This perspective begins to change when he is defeated in a fair race by the Seiba brothers during a competition at Mikuni's Five Star Land. Finding genuine enjoyment in the spirit of regular, non-combative racing, J makes a pivotal decision. He renounces the destructive battle-racing ideology of Dr. Ogami and leaves the Ogami Labs for good.

Seeking a new path, J goes to live with Dr. Tsuchiya, the benevolent pioneer of Mini 4WD development, and becomes his assistant at the Tsuchiya Racing Factory laboratory. This transition deeply affects his personality. Having lived a reserved and isolated life under Dr. Ogami's harsh tutelage, he is initially an introvert. Over time, however, he blossoms into a much more cheerful and soft-spoken boy, finding a sense of belonging and purpose within his new circle of friends.

Within the main group of racers, J is distinguished as the most skilled technician and mechanic. His prior experience with computers and advanced machinery during his time in the Ogami Corps serves him well in this capacity. His mechanical prowess is demonstrated on several key occasions. He famously repairs a badly damaged Tridagger X as a way to repay his friend Ryo for a previous racing incident. He also plays a crucial role in helping Go design and build the high-performance Cyclone Magnum. Perhaps most significantly, J is the designer of the Proto Saber EVO, a testament to his engineering abilities. He forges a particularly close bond with Go, who becomes his best friend among the team.

J's history and expertise also give him a unique perspective on the hobby of Mini 4WD racing. He has a notably sentimental and sympathetic connection to his own machine, perhaps valuing it more as a partner than a tool. This is especially evident when his Proto Saber EVO is put at risk by the actions of rivals, showing that his investment in racing is deeply personal. Among his key relationships, his mentorship under Dr. Tsuchiya is transformative, providing him with a positive role model and a stable home. J is also a core member of the team that represents Japan in the World Grand Prix tournament, where his technical skills are essential to their success. His development arc is one of the most clear in the series, moving from a brainwashed pawn of a villain to a valued, cheerful, and integral member of the heroes' team.