Vampire x Human
Wizard/Mage x Witch/Mage
Hunter x Supernatural creature
Best Friend x Best Friend's Sister
Bodyguard x Guarded
Cop x Criminal/Informant
Gang Member x Rival Gang Member
Gang Member x Innocent civilian
Good Girl x Bad Boy
Professor x Student (College only)
Professor x Teachers Assistant
Pirate x Mermaid
Prince x Commoner/Concubine
King/Prince x Queen/Princess/Sorceress from Conquered Kingdom
Knight x Princess/Mage/Sorceress
Lord/Lady x Staff
Outlaw/Mercenary x Bounty
Superpowers x Normie
Sorry, my taste is trash.
Best Friend X Best Friend's Sister
A and B have been friends since childhood. They went to the same schools since kindergarten, have played sports together both on school and outside teams. They shared everything, spent countless nights together at sleepovers, each respective kid's family becoming like a second family to the other. As such, they knew each other's siblings almost their whole lives, became like siblings with them. In early high school, B's family split up. He opted to stay in the house he grew up in, living with his mom. He was privy to the reason for his parents' divorce and wanted nothing to do with his dad. His dad left and B refused to go visit, even when the courts tried to force him on his dad's behalf. Eventually his dad gave up, with only B's younger sister C living between the two parents' homes. It was like that for years, then C returned. Dad was getting remarried and the new step-mother was a witch. She couldn't stand C, and C couldn't stand her. Having hardly seen each other but a handful of times in years, it came as a surprise to A when his best friend's sister reappeared and she wasn't a kid anymore. He never imagined he'd be looking at his best friend's kid sister as a woman, or a viable option, but he is; and she's not exactly ignoring him.
It could very well be A's family that split up. Or perhaps either character's parents died and they were forced to leave to live with a relative, until they were old enough to go off on their own. Definitely some serious wiggle room here.
Superpowers x Normie (or anything for that matter)
This doesn't exactly pertain to superheroes or heroines, but does have peoples with powers or superhuman abilities, so it's kind of in line with that. You could defo liken this to Captain America: Civil War in a few respects, albeit perhaps only vaguely. Anywho, this is more of a rough concept than any kind of fleshed-out idea. You got all these people with powers in a city, naturally they're going to cause some destruction, right? Whether on purpose or by accident, shit happens. The government, the police forces and other public services naturally aren't fans of this. When chaos breaks out and things get broken, someone needs to be held responsible. That way, the city isn't losing so much money fighting a losing battle, constantly having to clean up the messes these individuals make. So, within the police department, they created a specialty unit that is trained and equipped specifically to deal with these powered individuals. Once caught, they go through the typical legal system, while also being registered in a specialty database that catalogs their identity and powers to make them more easily identifiable and catchable should they commit powered crimes. There's a major rift between peoples and the ideologies around powers. Some think that registration is necessary, so people can be held accountable. Others are vehemently against it. If regular people don't have to be registered, why should powered people? You have powered police officers, too, not just general citizens or criminals. So, there are different peoples and viewpoints on al sides. As such, you also have a big syndicate doing deals with anyone and everyone of power under the table. Paying government officials to look the other way and protest registration, since the syndicate is run by a powerful man. Pun intended.
There's not really a limit to what you could do in terms of a character. I do have a character in mind for this, who has a brother working for the special force as a person of rank. He's been looking for her, but she's done a pretty good job of flying under the radar. Still she protests with other powered people and may not go free for much longer.
King X Queen/Princess/Sorceress/Concubine
This one could easily be smashed together with the first two, in a way. A king, whether mortal or magical, conquers a neighboring kingdom and takes the highly-prized lady into his own castle for whatever reasons he may have. Be it as a trophy, an addition to a harem, to serve as part of his magic-wielding army. Kind of makes me think back to a manga called Red River, where the female lead Yuuri was whisked across time and space to ancient Anatolia to be a live sacrifice to the evil queen who was trying to kill the King Mursili's sons, so her son (the youngest and last in line) could be next in line for the throne. Well, Yuuri gets rescued by Mursili II, Prince Kail, and he takes her into his home under the guise of being a concubine in his harem, though there's actually a separate house just for the harem. The other girls are jealous that she gets to live in the main house. Not only is Yuuri Kail's new favorite, but he also needs to keep her close to protect both their lives. Could defo take a similar route to that or whathaveyou.