Miyuki Kobayakawa is the bookish, mechanical, smart one of the pair. She drives the police car. She invents the weapons, soups up the vehicles, etc.. She is sweet on Nakajima.
Natsumi Tsujimoto is the rowdy, outgoing, strong one of the pair. She drives the motor-cycle. She has super-human strength from her father, who is a professional wrestler. She is sweet on the Captain. Note: Her name is pronounced "Natsumi", even though it's spelled (by the author) without the 's'. I've included the 's' so English speakers don't get in the habit of mispronouncing the name...
Nakajima is a large, sincere, motorcycle cop. He becomes Miyuki's boyfriend. His dad is Daimaru.
The Captain. Natsumi develops a serious, and reciprocated, crush on the captain as the series progresses.
Futaba Aoi is a male police officer who dresses and acts like a woman. Before he came to Natsumi & Miyuki's precinct, he worked in the anti-rape squad. His job was to dress up as a woman and act as a "decoy" for rapists. As time went on, he discovered he liked being a woman. She's called Aoi-chan by the other characters.
Daimaru is Nakajima's father. Daimaru 's a Hell's Angel type. (Not a criminal, just a rough biker dude.) He taught Nakajima everything he knows about riding a motor cycle.
Yoriko. Another police woman. She's a bit of a nerd. She wears glasses, rides a bicycle to work. Yoriko doesn't have a boyfriend.
Satori-chan. She was originally introduced as a suicidal teen-ager. But then she was inspired by the heroines. See File 17 She decided to become a police officer. See File 44
Strike Man is the arch villain of the series. He always wears a baseball uniform, a hood, and a cape. Strike man is not actually very evil, more sort of chaotic neutral. Full Page Strike Man