Crossover Love
I'm sure you'll agree with me that Kingdom Hearts is the perfect crossover material. You can pull almost any crossover you can imagine just by using the "It's a world infected by heartless, so Sora arrives there in his gummy ship to kick their asses" plot-device.
Why is there a lack of Crossover love in this fandom, then? It's a pity that they are so hard to find (and the few I've found at FF.net are mostly High School AU's that don't follow the plot from either universes).
But really, Crossovers are extremely fun to plot! The key is to find common traits between the two (or more) fandoms involved, and I asure you that the plot ideas will appear like magic. These traits can be related to the main plot of both fandoms, the characters' looks and personalities (jobs, history), daily life in both universes, etc. The possibilities are infinite!
And since I'm afraid I'm not making sense, I'll just better show you some examples of common traits that could be used for crossovers between three of my main fandoms and Kingdom Hearts: Tales of the Abyss, The Legend of Zelda (Twilight Princess) and Digimon 02.
Spoiler free (unless marked behind a link).
Kingdom Hearts and Tales of the Abyss
These are Luke and Guy, main characters from Tales of the Abyss. They're best friends, just like Roxas and Axel. Both Axel and Luke are selfish jerks. Guy and Roxas have different personalities, though.
That's an stupid example, I know, but on the other hand, there's a plot-related trait the these fandoms share, and IMO it'd make an awesome crossover. Here's the link for the ones who have played ToA up to the first visit to Yulia City.
Kingdom Hearts and The Legend of Zelda: Twilight Princess.
(I've only finished the fourth dungeon, so I don't know if there are other common traits between these two games)
Once upon a time, there were a couple of light universes that lived peacefully. One day, evil shadow creatures invaded the land with the sole purpose to cover it with daaaaarkness. OH NOES!
But don't worry! Because both Hyrule and the Disney Universe have Heroes chosen to carry the only weapons who can deflect the dark powers and destroy evil!
They both have the ability to transform into beasts!
And they both have a kick-ass toys! (Spoilers for TP Fourth dungeon's main item).
And I've just realized that both Sora and the Link from OoT like to take loooong naps (and transition through puberty while sleeping).
Kingdom Hearts and Digimon 02
Meet the main characters. They both are 14-15 years old, have spiky brown hair, cheerful personalities and believe that the best way to deal with computers is kicking them. Both were chosen to save their worlds from darkness. Both have digital friends (Digimon and Tron) and travel to their digital worlds with the help of a computer.
These are Kari, Chosen Child of Light, and Kairi, Seventh Princess of Heart.
They are special, therefore the perfect targets for the forces of daaaaarkness. Well... at least the heartless don't want to reproduce with the help of Kairi :S.
And they both like to spend time at the beach, waiting for their best friends (and in the end, it's the bond between their hearts what reunited them).
And yep, these fandoms both have the angsty "pretty boy" who was invaded by the darkness, but in the end realized that what they were doing was wrong, felt guilty about their past actions and tried to help the heroes from the distance, because they didn't feel worthy of their friendship. Of course, the heroes had to knock some sense into them :D.
They both weren't supposed to exist :(.
And finally...
(Errr...this is not crossover material XD),
In conclusion, there are endless possibilities for crossovers, you just need to figure out the common traits between the fandoms.
Crossovers need love too!