Koji is a friend and fellow motorcyclist of Shingo Mochizuki. He is both short-tempered and mean. He tunes his own motorcycle and brags about it, just like Shingo. He sticks to Shingo like glue and the two are always hanging around together. He is almost always rude when talking to people, except when addressing skilled mechanics like Goro Ono.
- Koji's zodiac sign is Aries and he has a B blood type.