Minsons

Han Jisung was born into a dysfunctional family and this played a big role in his future.
His father died quite early, and his mother was, frankly speaking, a whore.
Because of this, Jisung was bullied at school. In his class, there was a group of people, the leader of which was Park Hee-kyung. They mocked Han, saying they were just "joking," but was it a joke how they regretted that Jisung remained alive after such "games"?
Jisung grew up without telling anyone what happened. His mother ran away with some guy when he was a child, so he definitely wouldn't have told her.
Jisung started working in the police, but even after he started working there, he didn’t try to find his offenders. He couldn’t, because to this day he had nightmares about what happened.

Jisung was problematic. He was often rude to those he shouldn't have been, and sometimes he would lash out at people he caught at fault.
Because of this, he was transferred to a small town, to a different station.
There he was given to the eldest hyung, Lee Minho, as a new junior partner.
Minho wasn't happy that now some junior was investigating the murder with him. Because now, if Jisung did something, Minho would be held responsible for it.

But...Jisung didn't know yet that the prosecutor,
The one who is trying to take the case away from the Minsons is that same Park Hee-kyung.

(You can be Jisung or Minho)