One possible plot could be that Sora and his friends land in the underwater world of The Little Mermaid. Ariel could be in trouble, perhaps captured by the Heartless. Sora, with his Keyblade, would fight to free her. Donald and Goofy could help by using their magic and strength respectively. They would then have to find a way to restore the underwater kingdom's heart which has been affected by the Heartless presence.
Sora would likely be very protective of Ariel. He would see her as someone in need of help, just like he does with many characters in different worlds. Ariel, on the other hand, would be fascinated by Sora's world and his Keyblade. She might ask him a lot of questions. Donald could get frustrated with Ariel's overly curious nature at times, while Goofy would just be friendly and go along with whatever is happening.
One idea could be to explore what would happen if Sora and his friends got trapped in Ariel's underwater world during a Heartless attack. They'd have to team up with Ariel and her friends to fight off the Heartless while also dealing with Ursula's schemes in a new way.
Ursula is an obvious choice as she is the main villain in the original Little Mermaid story. In a Kingdom Hearts fanfiction, she could be even more powerful, perhaps having made a deal with the Heartless or some other dark force to gain more control over the underwater world and other worlds connected to it.
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.
Another aspect could be how Sora's presence affects the balance of power in the My Little Pony world. His powers are quite different from what the ponies are used to. The villains in the My Little Pony world might see Sora as a new target or a threat. Meanwhile, the ponies might look up to Sora as a new hero, and his actions could inspire them to be braver and more adventurous in protecting their own world.
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.
Imagine a fanfiction where Moana and the Little Mermaid embark on an adventure to a mysterious island in the middle of the ocean. This island is said to hold the key to a powerful magic that can heal any damage to the ocean. Moana would be excited to explore the island, while Ariel would be a bit more hesitant as she is used to the underwater world. But once they land, they discover that the island is full of strange and wonderful things. They meet creatures that are part - plant, part - animal, and they have to solve puzzles to get closer to the magic. Their different perspectives and skills would make this a thrilling and unique adventure.
Another theme is friendship. Sora is all about making friends, and in crossovers, he forms new bonds with characters from different franchises. For example, he might become friends with Sonic the Hedgehog and they team up to fight a common enemy. It shows how his positive attitude can bridge different universes.
There are quite a few. One interesting one might be on FanFiction.net. You can search using the tags 'Sonic' and 'Kingdom Hearts' to find crossovers that combine the high - speed, energetic world of Sonic with the complex and magical Kingdom Hearts universe. It's always fun to see how authors blend Sonic's speed and his friends' abilities with the Keyblade - wielding heroes of Kingdom Hearts.