Koko is the oldest of the trainees and, unlike her friends Wilson and Brewster, is powered by electricity, meaning she only needs to charge her batteries every now and then, as opposed to fueling up with diesel. Koko tends to be rather overconfident and rush through things, but unlike other fast passenger engines, she doesn't mind hauling freight, and does works as hard as she can. She cares deeply for her friends, and will always apologize and help them out whenever she's done something wrong.
Koko appears to be a freelance design with no specific prototype. However, her shape seems to loosely resemble to the bullet trains built between 1961-1986 in Japan, most notably the 0 Series Shinkansen.
Koko is painted green and white on her body with purple lining and underbody.
- Koko is the oldest of the three trainees, although the actual Shinkansen bullet trains were not built until around 1961-1964, making Koko younger than Wilson and Brewster.