Sora would be really interesting. He has such an innocent and determined nature in 'Kingdom Hearts'. In the 'Once Upon a Time' setting, he could be the one to bring a sense of hope and adventure. His reactions to the different fairy - tale characters and settings would be fun to explore.
I think Riku would also be a great character to focus on. He has that complex backstory of his struggle with darkness. In the 'Once Upon a Time' world, he could face new temptations or find new ways to redeem himself. Maybe he gets involved with a character like Hook and they have to learn to trust each other while dealing with the threats in the new universe.
Sora and Henry. Henry is always looking for adventure and has a connection to the storybook world. Sora could show him more about different worlds and how to fight using the Keyblade. They could form a really cool mentor - mentee relationship.
Sora would be a great choice. He's already a central character in the Kingdom Hearts series. In a Keyblade Wars fanfiction, seeing how he adapts to the chaos of the war, his moral compass in the face of such a large - scale conflict, and how his relationships with other Keyblade wielders change would be really interesting.
Sora would be really interesting. His naivete and pure heart could be a great contrast to the dark and gritty world of Blade. He would probably approach the vampire - fighting situation with his usual optimism and might even try to find a way to redeem some of the vampires, thinking they are like the lost souls he has saved in the Kingdom Hearts worlds.
Naruto would be very interesting. His boisterous personality and his strong sense of justice would make for great interactions in the Kingdom Hearts universe. He could be constantly amazed by the different worlds and the magic in the Kingdom Hearts setting, and his growth as a character could be explored further as he faces new challenges outside of his own world.
Hermione would be a great character to focus on. She is intelligent and curious. In a fanfiction involving the Heartless from Kingdom Hearts, she would be the one who would immediately start researching about them. She would try to find any connections between the magic in the Harry Potter world and the existence of the Heartless. Her thirst for knowledge would lead her to make some interesting discoveries and she could potentially come up with unique ways to combat the Heartless using magic spells and potions.
A really popular one is 'Heart of the Enchanted Forest'. This fanfic delves deep into how the Heartless could potentially invade the Enchanted Forest from Once Upon a Time. It has some great action scenes with characters from Kingdom Hearts fighting alongside the heroes of Once Upon a Time. For example, Riku teams up with Prince Charming to battle a horde of Heartless that are threatening the forest.
Another plot idea is a crossover of the villains. Imagine Maleficent from 'Kingdom Hearts' teaming up with the Evil Queen from 'Once Upon a Time'. They could combine their powers and knowledge to try and take over all the worlds. The heroes from both universes would then have to work together, which would lead to some really interesting character interactions and battles.
I think Lincoln would be the most interesting. He's used to handling a big family and all kinds of chaos at home. In the Kingdom Hearts universe, he could use his adaptability and problem - solving skills. He'd be curious about the new worlds and the magic there, and his journey of discovery would be really engaging to read about as he teams up with Kingdom Hearts characters.
One idea could be that Sora and his friends get transported to the Once Upon a Time realm. They could team up with Emma Swan to fight against the Heartless that start to invade Storybrooke. Maybe the Keyblade can be the key to unlocking some of the dark secrets in the town's past.
Sora and Spider - Man would be a really cool pairing. Sora has his acrobatic skills with the Keyblade, and Spider - Man is all about agility and using his webs in combat. They could have a great time swapping stories about their different worlds and learning new moves from each other. For instance, Sora could teach Spider - Man some basic Keyblade forms, and Spider - Man could show Sora how to use his environment better for combat, like swinging from buildings.