Kai Kogashiwa is a street racer from Tochigi prefecture, and a son to a legendary Downhill ace and Bunta's rival, Ken Kogashiwa. Ken taught Kai in the racing world from a young age, participating in karting competitions which made him specialized in midships (colloquial term for mid engine, rear drive). Before his transition to street racing, Kai was the fastest motorcyclist on Irohazaka. It can be seen that Kai's specialty on Irohazaka is similar to Takumi on Akina as he lives at Lake Chuzenji (which is at the top of Irohazaka) and takes the road during his daily commute to the bottom.

Kai had challenged Takumi on the Emperor's home course of Irohazaka. Kai had defeated Seiji Iwaki of Emperor and wanted to defeat Kyoichi as well, but set his sights on Takumi after Sudo's defeat. Kai uses a trick taught to him by his father to overtake Takumi by jumping a turn in a break in the guard rail on 33rd corner. However, he spins out on the final straightaway after his car loses traction from landing on leaves on the side of the road and was defeated.

Kai reappears as an opponent for Project D in Kanagawa prefecture. Kai represents the downhill ace for Racing Team Katagiri against the Eight-Six. However, he spins out at the last sector costing him the race.

Originally, Kai drives his father's Toyota SW20 MR2 but later switches to a silver Toyota MR-S ZZW30 (3rd Generation MR2 Roadster), leaving the SW20 to his father.

(Source: Initial D Wiki)