I have a few vague ideas for RPing one of those three settings, but I can't really decide which one, so I thought I'd offer it as a vote. Here are the candidates:
1. Avatar - The Dying Art: The Korra series opened up a slew of possible ways for the Avatar world to evolve. The premise is that the world has come a long way since the days of Avatar Korra 200 years ago. However, with the death of Hiroshi, the Avatar who succeeded Korra, no new Avatar was born among the Fire Nation. Had the line been broken somehow? No one really knows. Nevertheless, technology continues to grow, and as it does, the ancient arts of Bending slowly diminishes in its wake. Where Benders were the dominating force of the old Hundred Year War and at the pinnacle of debate during the Equalist Crisis, now they seem to be all but extinct. Only the most dedicated of traditionalists still remember the ways of the Earth, Fire, Water, or Airbenders. Our characters would be young people who have discovered that they can move the elements and, in a world that has all but forgotten the Art of Bending, they must seek out someone, somewhere, who shares their ability or at least can tell them more about it, especially with the threat of war from the World Empire. The World Empire originated from Republic City, once thought of as the center of equality and democracy in the world, but just under twenty years ago it was reorganized into an Empire, and now threatens to the swallow the surrounding nations into its control.
2. Legend of Zelda - Hyrulean Wasteland: This one isn't as fleshed out, yet, so I'll need some help/suggestions for setting it up, but the basic premise is that during one of Ganon's many stints at invading the land, the Hero of Time mysteriously never appeared. As such, Ganon ruled Hyrule without challenge... or he would have, if it weren't for a miraculous bit of divine intervention. The three goddesses, unable to allow Ganon to rule so freely and unopposed, decided to stop them by their own means. Here is where the story sounds kind of familiar, because in Wind Waker this was how the world was flooded and came to be the Great Sea. Not so in this storyline. Rather than drown Ganon in a sea of water, the goddesses instead destroyed him with fire raining from the heavens. Of course, such power cannot be unleashed on the land without consequence, and so Hyrule, despite being "saved" was in fact destroyed. Cut to about 70 years later, and Hyrule's descendents now live in what's left of the kingdom, scavenging old towns or villages for equipment, food, or the like. This is where the suggestions come in because, while I thought out the setup and the premise, I'm still pondering what kind of plot to give a setting like this. Perhaps Ganon somehow returns? Perhaps a quest is started to find a fabled relic supposedly able to restore the land? Maybe a little of both? I'm not really sure.
3. Kingdom Hearts - Shadows of War: In this we play as a generation of characters that immediately followed the events of the Keyblade War. In other words, we're talking about a prequel that predates even Birth by Sleep. Think of it as a Kingdom Hearts version of Knights of the Old Republic, where we can play as a Keyblade Wielder (called "Bladers" in-universe) or non-Blader on a quest to understand the tragedy of the Keyblade War and why the World Order must be protected... or to start the war all over again. This would, theoretically, be an RP where one could use Light or Darkness as their source of power and, if they wish, follow their own ambitions if the oath to protect the World Order doesn't fancy them.