One idea could be that Sora and his friends end up in Equestria. They could team up with the ponies to fight a new threat that is affecting both their worlds. Maybe the Heartless are somehow being drawn to Equestria's magic and they need to find a way to stop it together.
Riku could also play a major role. His more complex and sometimes brooding personality could add an interesting dynamic. He might start off as a bit of an outsider in Equestria but eventually come to understand and care for the ponies, especially if there are some ponies who remind him of his friends from his own world.
One interesting plot could be that the ponies from MLP accidentally find themselves in the Kingdom Hearts universe. They might mistake the Heartless for some kind of dark magic creatures from their own world and try to fight them using their magic. For example, Twilight Sparkle could use her powerful spells to combat the Heartless while trying to figure out how to get back to Equestria.
The Keyblade wielders like Sora, Riku, and Kairi would bring a sense of adventure and a different kind of magic to Equestria. The ponies, on the other hand, could teach them about the power of friendship in a more direct way. Donald and Goofy might be a bit startled by the ponies at first but would soon get used to them. Donald's magic could be compared to the magic of some of the unicorn ponies, and they could exchange magical knowledge.
The idea of friendship is also quite common. Since MLP is big on friendship, fanfictions often use that concept within the context of Kingdom Hearts' more battle - and adventure - oriented world. For example, the ponies' friendship might be a source of power against the darkness in Kingdom Hearts. And also, the concept of different worlds is shared. Just as Kingdom Hearts has various Disney - inspired worlds, MLP's Equestria can be seen as another world in the Kingdom Hearts universe in these fanfictions.
One great 'Kingdom Hearts Crossover Fanfiction' is 'Kingdom Hearts and Final Fantasy: The Convergence'. It combines the elements of Kingdom Hearts and Final Fantasy in a really interesting way. The characters from both universes interact in a believable manner, and the plot keeps you hooked from start to finish.
Twilight would be excited to explore a new fictional universe. She'd start taking notes on the magic systems and different worlds in the fanfiction. Rainbow Dash would be bored if there wasn't enough action. She'd be looking for epic battles and heroic deeds. Pinkie Pie would love the fanfiction just for the fun of it, no matter what it was about.
First, you need to have a solid understanding of both universes involved. For example, if you're doing a Kingdom Hearts and Pokemon crossover, know the Pokemon types, their abilities, and how they interact. Also, be familiar with Kingdom Hearts' keyblade mechanics and the different worlds. Then, create a unique plot that ties the two together. Maybe the Pokemon are new forms of Heartless or something.
The fanfic often plays with the different powers and abilities. For example, the keyblades in the MLP world are a unique concept. The ponies might use them in ways different from how they are used in Kingdom Hearts, adding a new dimension to the story. Also, the magic in MLP and the magic in Kingdom Hearts can be combined in creative ways in these fanfics. They might create new spells or ways of fighting that are unique to this crossover.
Sure. 'A Keyblade in Equestria' is a popular one. It combines the magical world of MLP with the keyblade -centric plot of Kingdom Hearts in an interesting way. The characters from both universes interact in a unique setting that makes for an engaging read.