There could be a fanfiction where Batman is somehow transported into the past of the Kingdom Hearts universe. He has to use his wits and skills to survive in a world that's very different from his own. Maybe he teams up with young versions of the Keyblade wielders. He could teach them about his style of combat and investigation, while they introduce him to the magic of hearts. This would be a great way to explore character growth for both Batman and the Kingdom Hearts characters.
A creative plot could be that the villains from both universes team up. So, the Heartless along with some of Batman's classic foes like the Joker or Two - Face. The heroes from Kingdom Hearts and Batman would then have to combine their powers and skills to take them down. It would be a battle of different powers and ideologies.
One creative plot could be the characters from Kingdom Hearts finding themselves in the Resident Evil world. Sora, Donald, and Goofy might have to use their Keyblades against the zombies and bio - organic threats. They could team up with some of the Resident Evil protagonists like Leon or Jill to find a way back to their own world while also trying to stop a major outbreak.
The fanfiction 'Sora's Portal to Parallel Worlds' is extremely creative. It has Sora finding portals that lead to parallel versions of the Kingdom Hearts worlds he knows. He has to deal with different versions of his friends and enemies, and it really makes for an interesting read. 'Sora's Elemental Awakening' is also very creative. Here, Sora discovers that he can control all the elements, and he has to learn how to use them properly to save the Kingdom Hearts universe from a new threat.
One cool plot idea could be the Loud family getting transported into the Kingdom Hearts universe. Lincoln could team up with Sora to fight the Heartless. Maybe the sisters would each have a unique role, like Luna using her music skills to soothe some of the more aggressive enemies. Another idea is that the Keyblade could choose one of the Loud siblings as its new wielder, leading to a whole adventure of them learning to use it and save both their world and the Kingdom Hearts worlds.
In some fanfictions, the Keyblade wielders could learn from Batman's detective skills. Picture Aqua learning Batman's stealth techniques. This could add a new layer to her character. And vice versa, Batman could be intrigued by the power of the Keyblade and the concept of hearts. There are so many possibilities for character development and unique storylines in these Kingdom Hearts - Batman fanfictions.
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.
A really creative plot is the one where Naruto and Tatsumaki are in a world where their powers are swapped. Naruto has to deal with Tatsumaki's psychic powers and her reputation in her world, while Tatsumaki has to figure out how to use chakra and live as a ninja. It's full of humorous moments as they struggle to adapt to their new powers, but also shows how they can grow and learn from each other's experiences.
A really creative plot is in a fanfic where the Leviathans can possess animals as well as humans. It makes for some really strange and unexpected encounters for Sam and Dean.
One creative plot is an orc - led environmental movement in fanfiction. Orcs, usually seen as war - like, are the protectors of nature. Another is orcs and humans swapping bodies and having to understand each other's cultures from a very different perspective. And the plot where orc tribes form a democratic society is also quite out - of - the - box.
A plot could be that Godzilla's DNA is used in some crazy experiment in the Naruto world and it creates a hybrid creature with ninja abilities. This new being has the strength of Godzilla and the stealth and jutsu skills of a ninja. It would be a very powerful and unpredictable character in the fanfiction.
A creative plot could be where Hermione uses her magic to help Riddick control his 'Furyan' side better. For example, in some fanfics, she creates spells that can soothe his inner rage. This is interesting because it combines the magic system from Harry Potter with the unique biological aspect of Riddick.