Car: Mitsubishi Lancer Evolution IV RS (CN9A) (color: scotia white)
Seiji Iwaki is the number two driver in the Lancer Evolution-only Emperor team, therefore he drives the Lancer Evolution IV. Seiji is a driver with good racing skills, but he is rather arrogant and overconfident and occasionally imprudent. He has won many races driving for Emperor against other teams, including Takeshi Nakazato of the NightKids and a member of Thunder.
After defeating various teams in Gunma, the Emperor team then set their sights on the Akina Speed Stars, aiming to beat Akina's infamous Eight-Six. Seiji volunteered to race for the Emperor team in his Evo IV against Takumi's Eight-Six, but he was humiliated when his overconfidence and impatience led to his downfall, causing Kyoichi, the team leader, having to race the Eight-Six before the team could move on to the next opponent. It was also verbally stated that Seiji lost to Kai Kogashiwa in Irohazaka, but no actual battle was shown in the series. In Battle Stage, his Evo IV also raced Keisuke's FD, and lost.
One of Seiji's trademarks is to take the team sticker of teams he has defeated, cut it in half, and stick it on the sideblade of his spoiler upside-down, emulating the "kill" markers that fighter pilots paint on their planes.