Authority.
As the former tenth-generation leader of the Black Dragon, Inui had control over a massive army of strong delinquents. Later, as he becomes Taiju's assistant, he still has authority over the gang's members, though to a lesser extent.

Fighting Abilities.
Inui was unrivaled in a fight before meeting Taiju. Thus, he is a strong fighter in his own right.

Mechanical Knowledge.
As an ardent follower of Shinichiro, Inui inherited an abundance of mechanical knowledge from the bike expert.