Naoya Nitta is a killer consultant operating in Fukuoka, specifically the Hakata district. He is an old classmate of Shunsuke Saruwatari and works closely with him to help Saruwatari establish a reputation in the city's underworld. Nitta is also a member of the Kokura Fried Wings baseball team, which is known as the Ogura Fried Udons in the anime adaptation.

After high school, Nitta abandoned a conventional lifestyle and applied his sharp social skills and business instincts to become a consultant for hitmen. He offers his services to figures such as George Gondo, acting as a strategist and intermediary for assassination jobs.

Nitta is intelligent and strategic, possessing a calm and analytical demeanor. He dresses in professional attire, typically wearing silver-framed glasses, a deep blue jacket, necktie, pinstripe shirt, and white chino pants. He always carries a small handgun for protection, though his primary strengths lie in planning and coordination rather than direct combat.

He appears as a supporting character in the series, interacting with various underground professionals. His relationship with Saruwatari is central to his role, as Nitta’s motivation is largely driven by helping his old friend succeed in Fukuoka’s competitive criminal landscape. His development is limited in the anime, remaining a steady and reliable figure who facilitates operations behind the scenes. Notable abilities include his strategic planning, network of contacts, and skill in managing assassination contracts.