Yuichi Tachibana is the boss of the gas station that Takumi worked in. An old friend of Bunta's and a racer in his youth, Yuichi acts like a father figure to the "Akina Speed Stars".
It seems that he drives a black Toyota Chaser that is seen during some of Takumi's races that he watched, specifically the races against Nakazato's R32 and Ryosuke's FC3S.
(Source: Initial D Wikia)