You can often find such fanfiction on dedicated fanfiction websites. Some popular ones include Archive of Our Own. Just search for 'Young Xehanort and Eraqus' on the site, and you'll get a list of relevant stories.
A fanfiction might focus on a journey they took together. They could be on a quest for a powerful artifact. Along the way, they face various challenges that test their friendship and their understanding of the Keyblade. For example, they might encounter a group of powerful Heartless and have to combine their skills to defeat them.
One possibility could be that young Xehanort grabs Kairi as part of a plan to manipulate Sora. He might think that by having Kairi in his control, he can draw Sora out and into a situation where he can be easily influenced or defeated. This could lead to a series of events where the heroes have to figure out how to rescue Kairi from Xehanort's clutches while also dealing with his larger scheme.
Aqua, if she were involved, would be determined to save Kairi. She has a strong sense of justice and protecting the innocent. She would likely use her magic to try and track Xehanort and Kairi. Donald and Goofy would be loyal to Sora and follow him into the fray, but also try to keep Sora from making hasty decisions. They would offer their support in combat and also try to think of practical ways to free Kairi, like finding Xehanort's weaknesses.
Kairi could be looking for an opportunity to use her physical combat skills. If she can get close enough or find a moment of weakness in Young Xehanort's grip, she might try to land a blow or use a self - defense move to break free. She may have learned some basic combat moves from training with Sora and Riku, and she could be relying on those in this situation.
Power is a common theme. Xehanort is often a power - hungry character, and in crossovers, his pursuit of power is pitted against the powers and rules of the new universe he enters. For example, if he crosses over into a universe with a strict moral code regarding magic use, his power - hungry ways will be challenged.
One possible reason could be that Young Xehanort is very powerful. His strength might be overwhelming for Kairi, both physically and in terms of his dark magic if he uses it against her. Another reason could be that Kairi is in an unfamiliar situation. Maybe she's in a strange place or time where she has no allies to help her, which makes it difficult for her to fight back against Young Xehanort's grip.
There's also 'Xehanort's Journey through Kingdom Hearts Crossovers'. This fanfiction takes Xehanort on adventures across different Kingdom Hearts - like worlds that have been cross - overed with other game universes. It's interesting to see how Xehanort's dark plans are affected by the new environments and characters he encounters.
I'm not entirely sure. It could be a very niche or even a made - up concept by a small group. Harry Potter and Xehanort are from two very different fictional universes (Harry Potter series and Kingdom Hearts respectively), so it might not be a mainstream or widely recognized fanfiction idea.
Well, one possible plot could be that Xehanort's essence or some form of his power gets transferred into the Harry Potter world. This power could start to corrupt some of the wizarding community, and Harry, with his strong sense of right and wrong, has to trace the source of this new evil. Along the way, he discovers more about Xehanort's past and motives, and has to use his knowledge of both the wizarding world and Xehanort's methods to defeat this new threat. It would be a complex plot that would require a lot of world - building to combine the two very different fictional settings.