This challenge has you specify either one of your original universes or a fandom that you're working on. I picked the latter.
I've written in a lot of fandoms, but one of the most recent is Justified.
Justified is a character-driven TV show that runs on the FX network. Its main character is Raylan Givens, a U.S. Marshall with an itchy trigger finger. After a public shooting incident, Raylan is called back to the Marshall's office near his hometown in Harlan County, Kentucky. The office has a bombing case, and the leads point to a local troublemaker—surely Raylan can work his magic as the "Hillbilly Whisperer" and crack the case?
The suspect in question turns out to be someone Raylan knew while growing up in Harlan, the shrewd and enigmatic Boyd Crowder. Over the course of the show, Raylan and Boyd will have many more dealings, all of them colored by a combination of mutual distrust and the inability to stop liking each other despite how often their goals and motives are in direct opposition.
Raylan's upbringing colors much of his character. His father, a local petty criminal, drank too much, and he beat Raylan's mother. Raylan's choice to be a lawman is a complete rejection of his father, but in marrying Winona (they later divorced), he put himself at the mercy of someone who always disapproved of who he was. Raylan is patient in gathering facts, but he can be very short-tempered when dealing with people. When he fires his gun, he usually shoots to kill. All of his shootings thus far have been considered "justified" (hence the name of the series), but often just barely.
Boyd's father was a career criminal like Raylan's, but far more successful. Boyd alternates between truly wanting to become a better man and slipping right back into the family business (because it's what he knows, and he's good at it). There are times when it seems like he utterly adores Raylan, which is part of what motivates Boyd to change and also what keeps Raylan from completely giving up on him. Raylan can't bring himself to flat-out hate someone who loves him, or (in the case of his father, Arlo) someone who should love him but probably never has.
There's an electricity between Rayland and Boyd that hints at the possibility of them having had a deeper relationship in the past. They might have been close friends, or lovers, or had some kind of sexual fling. Speculating on that past is one of the more popular and open areas of Justified fanfiction.
There are a lot of marvelous minor characters, too. Raylan's boss, Art, is dry and hilarious, and his own patience is often sorely tried by Raylan's antics. Ava Crowder was an abused wife who one day hit her limit and solved her problems with a shotgun, and got to liking that approach very much. Raylan's aunt Helen is a mystery all her own: she knew her sister's husband was an abuser, and yet she married him after her sister died. She might have done it to help raise Raylan, and she certainly seemed to have a much more equal relationship with Arlo than her poor sister. But what brought her to take that first step, and to stay put after Raylan left home? Helen's history offers a rich area for fanfic writers to explore and invent.
I've written a couple of drabbles and a very short story in this universe, but I'm presently finishing out a somewhat longer story for the Hillbilly Remix and also working on a Justified/zombies story that will test my creativity in combining Raylan/Boyd slash with an unexpected uprising of visitors from the grave.
The show holds some of its fact close to the vest. It clearly takes place in a town, which is never named but is too big not to have a name. All we know is that it's part of Harlan County, an area where mining and drug-running live side by side, and where there are neighborhoods and realtors and hair salons and courthouses, and none of that will ever be enough to make certain residents happy.
Raylan Givens, in particular.