Natsuo Sawai is an A-class racer in the world of Dead Heat, a futuristic motorsport where competitors pilot FX machines, two-legged motorcycles equipped with arms that allow for both racing and physical combat. He is established as a top-tier superstar, widely admired by fans and younger riders alike. His personality is marked by arrogance and condescension, particularly toward lower-ranked racers; he dismisses the protagonist Makoto with insulting remarks when Makoto approaches him for an autograph before a major race. Sawai's primary motivation appears to be maintaining his elite status and demonstrating his superiority on the track, a goal he pursues with fierce competitiveness.

In the story, Sawai functions as the primary rival and benchmark for Makoto's ambition. Makoto, the rider of a struggling D-class team called Big Wave, dreams of reaching A-class and competing against racers like Sawai. Their rivalry culminates in the Open Cup race, where Makoto, after receiving a mysterious high-performance engine, manages to overtake Sawai and briefly take the lead before his machine fails due to the engine's incomplete tuning. Despite his earlier disdain, Sawai shows a grudging respect for Makoto's determination and skill, offering a compliment after the race and acknowledging Makoto's spirited performance. This moment represents a small but notable development in Sawai's character, revealing a capacity for recognizing genuine effort in others.

Sawai pilots a high-performance A-class FX machine, and his abilities as a racer are exceptional, combining precise control with aggressive tactics typical of the sport. He is also a public figure, a star whose reputation inspires both admiration and challenge among lower-tier racers. While his role is supporting, his presence defines the upper echelon that the protagonist strives to reach, and his eventual recognition of Makoto marks a key emotional beat in the narrative.