Shuichi Matsumoto is the personal mechanic for Takumi Fujiwara's AE86 and possibly Chief Mechanic for Project D. He is the driver for Project D's support van #3 during their expeditions.

In chapter 39 of the manga, Matsumoto was asked by Ryosuke to tune his FC for his anticipated encounter with Rin Hojo.

(Source: Initial D Wiki)