A crossover could involve the characters' quests. The characters in Final Fantasy 12 are often on a grand adventure to save their world or achieve a certain goal. Harry Potter characters could be inserted into this world and their Gryffindor - like courage could be put to the test in the dangerous and complex world of Final Fantasy 12. For example, Harry could join Vaan's group in their journey to defeat the Archadian Empire.
One interesting crossover could be the use of magic systems. In Harry Potter, magic is more about spells and incantations, while in Final Fantasy 12 there are various magicks like black, white, and green magick. A fanfiction could explore a character from Harry Potter learning the magick system of Final Fantasy 12, perhaps Hermione trying to study the more scientific approach to magic in Final Fantasy 12.
One interesting crossover could be the use of magic spells from Harry Potter in the world of Final Fantasy 7. For example, a character might use 'Expelliarmus' to disarm a Shinra soldier. Another could be the appearance of Final Fantasy 7 creatures in Hogwarts. Imagine a Chocobo running around the Quidditch pitch! Or perhaps a character from Final Fantasy 7 attending Hogwarts and having to learn about magic while also using their own unique abilities.
One interesting crossover could be the use of magic spells from 'Harry Potter' in the world of 'Final Fantasy XV'. For example, a character from 'Final Fantasy XV' might learn the Patronus Charm to fend off daemons. Another could be the appearance of Hogwarts - like buildings in the 'Final Fantasy XV' landscape. Maybe Noctis and his friends could attend a magical school similar to Hogwarts.
One interesting crossover could be the use of magic systems. In Harry Potter, magic is mainly done through wands and spells, while in Final Fantasy X, magic is more about summoning and using different elements. A fanfiction might combine these, like having a wizard in the Harry Potter world learn to summon aeons from Final Fantasy X.
Well, in some fanfictions, the characters' personalities might be combined. Cloud from Final Fantasy VII could be a student at Hogwarts with his brooding personality. He might be in Slytherin, using his skills with a sword (which could be magically enhanced) to protect the school. And Hermione could find herself interested in the technology of the Final Fantasy VII world, trying to figure out how the materia works and if it could be used in the wizarding world to enhance magic.
A cool crossover might involve the jutsu in Naruto being combined with the spells in Final Fantasy 14. Picture Sasuke using a spell like Blizzard III from Final Fantasy 14, but with his own Uchiha - style twist. Also, the ninja villages in Naruto could be compared to the city - states in Final Fantasy 14. The fanfiction could explore how the politics and power dynamics of both worlds interact when characters from each are forced to cooperate. Maybe the Hidden Leaf Village and Limsa Lominsa form an alliance to fight a common enemy that threatens both their existences.
One interesting crossover could be the characters from Naruto using the Materia from Final Fantasy 7. For example, Naruto with the Fire Materia could enhance his Rasengan with fire elemental powers. It would be a really cool visual to see.
One interesting crossover could be the combination of RWBY's unique combat styles with Final Fantasy's magic systems. For example, Ruby's scythe - wielding skills might be enhanced with some of Final Fantasy's fire or ice magic spells. It would create really dynamic and visually stunning fight scenes.
A crossover could involve the ninjas from Naruto's world being intrigued by the magic in Final Fantasy 7. Gaara's sand powers could be compared to some of the earth - based magic in FF7. For example, his sand might interact in interesting ways with spells like Quake. In a fanfiction, they could all participate in a tournament where ninjas and FF7 characters show off their skills, and Naruto and Gaara have to adapt their fighting to the different rules of the FF7 universe.
One interesting crossover could be characters from Final Fantasy having to navigate the political intrigue of Westeros. For example, Cloud from Final Fantasy VII might find himself in King's Landing. His combat skills could be put to use in the battles for the Iron Throne. He'd probably be a bit confused by all the backstabbing and political games, as he's used to more straightforward battles against Sephiroth and the Shinra.
A great aspect of a Final Fantasy 10 and Kingdom Hearts fanfiction crossover could be the character relationships. Yuna and Sora, for instance, could form an interesting friendship. Yuna's calm and spiritual nature might contrast and complement Sora's more impulsive and adventurous side. They could learn from each other's experiences, with Yuna teaching Sora about the summoning and the fayth, while Sora shows Yuna the power of the Keyblade and the importance of believing in oneself in the face of great evil.