Mechanic Miyaguchi is a supporting character in Initial D Fifth Stage who serves as a member of Project D's support staff and the designated mechanic for Keisuke Takahashi's Mazda RX-7 FD3S. She is a female mechanic with brown hair and black eyes, of Japanese nationality, and appears in the series from Fourth Stage onward. Her background is that of a skilled automotive technician who works behind the scenes to ensure the team's cars are in peak condition for their street races across the Kanagawa region. Miyaguchi is dedicated, professional, and quiet in demeanor, focusing on the technical aspects of the vehicles rather than the drama of the races. Her primary motivation is to keep Keisuke's rotary‑powered car running reliably and to adapt it to the demands of each opponent and course. She has a close working relationship with Keisuke Takahashi, as she is responsible for the maintenance and tuning of his RX‑7, and she also interacts with Ryosuke Takahashi, who coordinates the team's strategy. Throughout Fifth Stage, she remains a consistent presence, providing essential mechanical support without developing a dramatic personal arc. Her notable abilities include expertise in rotary engine maintenance, high‑performance tuning, and the ability to quickly diagnose and repair mechanical issues under the pressure of a competitive racing schedule. She also appears in Initial D Final Stage, continuing her role as Project D's mechanic.