I'm sorry, what is Kingdom Hearts?
It's a series of popular action-RPG videogames that combines every Disney character imaginable into one massive fantasy epic. It's kinda steam-punky and edgy, and has built up a huge following similar to how Nightmare Before Christmas was several years ago -- Really popular with under-35 Disney fans who like seeing classic animated characters with a bit of "darkness" and "edge" to them. Began in 2002.
In a nutshell, a young man name Sora joins forces with Donald, Goofy, (eventually) Mickey and a huge array of Disney characters like Beast and Jack Skellington to defend classic Disney worlds from the goonlike "Heartless," who are being helped by Disney villains. The fate of the entire Universe is at stake, and you get to travel everywhere from Steamboat Willie to Tron. It gets really, really dark.
Parkwise, it would make a swell dark ride, and the games' central hub "land", Traverse Town, would be a Fantasyland-type village with a steampunk/sci fi twist. Since the town is a refugee camp for Disney characters whose worlds have been taken over, literally any character could show up on the streets.
And that's Kingdom Hearts. Tried to keep it short.
A free mobile prequel called Kingdom Hearts Unchained X just came out on iPhone and Android. It's 2D (the main games are 3d modeled), and simplified, but captures the art style and music nicely.