One main theme is friendship. Just like in the original Kingdom Hearts and Pokemon, characters form strong bonds. For example, Sora might team up with Ash and they learn to trust each other.
There's a fanfiction called 'Kingdom Hearts: Pokemon Edition'. It takes elements from Kingdom Hearts like the Heartless and mixes them with the concept of Pokemon. The story follows a group of trainers who discover a connection between the two worlds and must fight to protect both. It has a really interesting plot that keeps you hooked from start to finish.
One popular 'Kingdom Hearts Pokemon fanfic' is 'A World of Keys and Pokeballs'. It combines the unique worlds of Kingdom Hearts and the Pokemon universe in an exciting way. The characters from both franchises interact in a well - written plot that keeps you engaged.
First off, think about what kind of story you want to tell in the Kingdom Hearts universe. Maybe it's a new adventure for the main characters or a side story about a minor character. Make sure your writing style matches the tone of the original series and keep the magic and fantasy alive throughout.
It might be seen as a fanfic because it combines elements from various Disney and Square Enix franchises in an unconventional way, appealing to fans' imaginations and creative reinterpretations.
One idea could be a crossover where Sora and his friends from Kingdom Hearts end up in the Pokemon world. They could team up with trainers to battle against the Heartless that have somehow invaded the Pokemon realm. Another idea is that some Pokemon could have the power of Keyblades, and they use it to protect their regions from both Pokemon villains and the threats from Kingdom Hearts like Organization XIII. Maybe a Pokemon like Pikachu could befriend Sora and they go on an adventure together to find a way to get Sora back to his own world while also helping the Pokemon world.
One idea could be a story where the Pokemon trainers are transported to the Kingdom Hearts universe and have to team up with Sora and his friends to fight against the Heartless. They could use their Pokemon's unique abilities in combination with keyblades to defeat the enemies.
One great fanfic about Roxas and Xion is 'The Bond Beyond'. It beautifully explores their relationship as they struggle with their identities within the Kingdom Hearts world. The author does an amazing job of delving into their emotions and the unique connection they share.
I really like 'Bleach - Kingdom Hearts: A New Alliance'. It has an interesting take on how the powers from both series would mesh. For example, it shows how a character from Bleach might use a Kingdom Hearts - inspired weapon in a creative way. The story also delves into the backstories of some characters more deeply, which adds a lot of depth to the fanfic.
Another area of advanced theory could be related to the connections between different worlds in the Kingdom Hearts universe. In fanfic, authors might postulate new ways that worlds interact, such as hidden portals or a shared energy source that links all the worlds together. This could lead to interesting plotlines where characters discover these new connections and use them to their advantage.