I’m gonna use Amber, since I’m feeling all Amberish of late. It almost writes itself. Peter Lepark is a Amber City resident who’s never been anything close to noble. One day, a friend of his who’s a groom at the Castle gives him a tour of the place. In the stables, Peter has a close encounter with none other than the Unicorn. The next morning, he wakes up with the ability to walk Shadow. Best not tell Oberon’s brood — they might not be too pleased.
The fun of this, I think, is in rephrasing the world in superhero genre terms. The royals are the Avengers, perched high above it all, big and muscular and just a little bit scary. Or more than a bit. Chaos is the X-Men — they say they’re out to do good but who can tell? The PCs are Peter and other street level types; Shadow dwellers with interesting abilities, highly trained second sons of Amber nobles who chafe against the limits of their birth; so on. This fits very well with the comic books, actually, since Spider-Man is established as having a certain cosmic tinge to his powers and Peter Lepark is the only one of the PCs with the abilities of Oberon’s line.
I’m imagining a campaign played large but not humorous. The concerns of the game are the concerns of the comics: fighting crime, dealing with individual problems. The royals have world-saving concerns, but the PCs don’t as much, although of course occasionally there’s an intersection.
I guess the Moonriders can fit in as the Inhumans. But the Moonriders can always fit anywhere one likes, no?