What are some interesting plot ideas for Kingdom Hearts Aqua crossover fanfiction?

One idea could be a crossover adventure where Aqua and Erza team up to face a powerful dark force. Maybe they start off as rivals, with Aqua's Keyblade skills and Erza's swordsmanship clashing in a misunderstanding. But as they realize they share a common enemy, they combine their powers. Aqua could use her magic to support Erza's more direct combat approach.

Well, a great plot could be Roxas finding himself in a crossover with a Final Fantasy world. He meets some of the iconic Final Fantasy characters like Cloud or Tifa. They initially suspect him because of his connection to the Heartless and Nobodies. But as they get to know him, they realize he's on their side in the fight against a new enemy that is trying to use the power of both the Kingdom Hearts and Final Fantasy universes. It could be a story full of action, character development, and exploring the differences and similarities between the two universes.

Well, perhaps in this fanfiction, the Organization XIII has a plan to use Elsa's powers for their own evil purposes. They manipulate events in Arendelle to make Elsa feel isolated and out of control. Sora, Donald, and Goofy show up and befriend Elsa, showing her that she can trust others. They then have to battle the Organization XIII members while also dealing with the internal struggles of Arendelle's characters, like Anna's determination to save her sister no matter what.

A possible plot is that the Soul Reapers discover the existence of Kingdom Hearts. They might think it's some sort of powerful spiritual object. Rukia could be the first to encounter a Keyblade wielder like Sora. Sora, in turn, could be intrigued by the Soul Reapers' powers and their way of dealing with the afterlife. The two groups could then join forces to stop a common enemy that threatens both their worlds. Maybe an ancient evil that wants to use the power of Kingdom Hearts and the souls in the Bleach universe for its own dark purposes.

One idea could be a story about Aqua's training in the past. It could explore how she mastered her keyblade skills, the challenges she faced, and the friendships she made during her training days. Another could be a story where Aqua travels to different worlds in the Kingdom Hearts universe in search of something, like a rare magic item that could help her defeat the darkness. And a third idea could be a story that focuses on Aqua's relationship with her friends, like Terra and Ventus, and how they support each other through difficult times.

Perhaps Voldemort discovers the power of the Heartless and tries to use them to his advantage. The protagonists from Kingdom Hearts then have to work with the Order of the Phoenix to stop Voldemort and the Heartless. The Hogwarts students could be fascinated by the Keyblades and the different worlds the Keyblade wielders have been to, and there could be a lot of cultural exchange between the two groups.

One idea could be that Sora and his friends end up in Equestria. They could team up with the ponies to fight a new threat that is affecting both their worlds. Maybe the Heartless are somehow being drawn to Equestria's magic and they need to find a way to stop it together.

One idea could be exploring the backstories of the new characters introduced in Kingdom Hearts 3 in more depth. For example, you could write about how they came to be in the different worlds and what their true motives are.

In a crossover fanfiction, Aqua could be paired well with Mickey Mouse. Mickey has a deep understanding of the Kingdom Hearts universe and his magic could complement Aqua's Keyblade abilities. They could embark on a journey together to uncover some ancient secrets that are crucial to both their worlds. Also, Elsa from Frozen could be a great pairing. Elsa's ice powers and her struggle with her own identity could find an interesting parallel with Aqua's journey and her powers. They could help each other grow and face challenges together.

One idea could be that the Heartless somehow find their way into the Marvel universe and start attacking various locations. The Avengers, being the protectors, team up with Sora and his friends from Kingdom Hearts. They initially have some clashes due to different fighting styles and ways of understanding the world, but eventually learn from each other and combine their powers to defeat the Heartless. For example, Iron Man could use his technology to analyze the Heartless' weaknesses, while Sora uses his Keyblade to directly combat them.