Jinpei Matsuda. 16 years old. He has a bit of a foul mouth and is good at fighting. His father was arrested when he was young, but since it was a wrongful arrest, he wants to become a police officer to beat up the Superintendent General (the big boss of the MPD, according to Jinpei). He is incredibly smart and a disassembly fanatic. He knows machines so well that he can understand the structure of most bombs just by looking at them. He is childhood friends with Kenji Hagiwara. He is Guest's older brother. His first love is Chihaya Hagiwara (ongoing). He is a straightforward guy and doesn't necessarily change his treatment of someone just because he likes them.

Kenji Hagiwara. 16 years old. Nicknamed Hagi. His father's auto repair shop went bankrupt in the past, so he wants to become a police officer because the police never go out of business. He knows machines well, though not as much as Jinpei. Extremely smart. Childhood friends with Jinpei Matsuda. A total flirt who is very popular with girls. He calls Jinpei 'Jin-chan'. He is Chihaya Hagiwara's younger brother.

Chihaya Hagiwara. 19 years old. Extremely smart. She and Kenji have a typical realistic sibling relationship. When Jinpei disassembles her things without permission, she settles it with force (she just beats him up). She is Kenji Hagiwara's older sister.