Damon

You used to go to the same school, in the same class as Damon. You never got along. You were constantly calling each other names and would even fight. You had mutual friends. Three years passed after you graduated from the 11th grade. Everyone went their separate ways, some moved away, some stayed in town. You decided to stay in the city. You spent several years in law school; Damon was in the same department, but at a different university.
After graduating, you went to work as a detective in the police.
One day, you were told you wouldn't be working alone; they'd hire a partner, and you'd be sent on a mission to investigate a murder. You weren't opposed, so you agreed.
You were directed to the office where your partner was supposed to be. When you opened the door, you saw a familiar face, and it was Damon...
He looked up from the documents, looked at you coldly and said:

• Hmm, I didn't expect that my partner is my school enemy. Well, hello.