One interesting crossover could be a scenario where the vampires from Vampire Knight attend Hogwarts. They would have to adapt to the magic system there. For example, their superhuman speed and strength might be an advantage in some magical duels, but they would also have to deal with spells like the Patronus Charm which they've never encountered. It could make for a really exciting story.
A crossover might involve the characters from Vampire Knight getting involved in the fight against Voldemort. Maybe the pure - blood vampires could have some sort of connection to the pure - blood wizards in the Harry Potter world. Their immortality could be a key factor in the battle, as they could outlast many of Voldemort's Death Eaters.
There could be a fanfiction where a character from Harry Potter, like Hermione, discovers the existence of the Vampire Knight world. She would be intrigued by their different form of 'magic' which is really more of a supernatural ability. She might try to study it and find ways to incorporate it into her own magical knowledge, leading to some very unique spells or potions.
A crossover might involve Sasuke from Naruto in the Vampire Knight universe. Sasuke's search for power could be paralleled with the vampires' thirst for blood or power in their own world. He could encounter the vampire hunters and perhaps form an unlikely alliance with them, seeing as he has his own vendetta against those he deems as powerful enemies. The idea of Sasuke using his Sharingan in a world full of vampires and their unique abilities would make for an exciting story.
A possible crossover idea is the characters from Harry Potter attending the Youkai Academy from Rosario Vampire. Imagine Harry, Ron, and Hermione trying to blend in with vampires, werewolves, and other supernatural beings. There could be a lot of humorous situations as they try to adapt to the different rules and cultures of the academy.
One interesting crossover could be a scenario where the yandere character from Yandere Simulator ends up in the Vampire Knight world. Maybe she becomes infatuated with one of the vampire characters. For example, she could target Kaname Kuran and try to eliminate any rivals in a very yandere - like way, all while dealing with the complex vampire society and politics in the Vampire Knight world.
Well, in 'harry potter x vampire knight fanfiction', a cool concept might be the introduction of Hogwarts students into the Cross Academy. It would be fascinating to see how they adapt to the day - night system and the different classes there. Also, the idea of a vampire attending Hogwarts secretly could bring a lot of drama. They would have to hide their true nature from the other students and teachers, and at the same time, learn magic. It could lead to some really intense storylines.
Well, in some fanfiction, we might see Anna and Kristoff visiting Hogwarts. They could be amazed by the moving staircases and magical creatures. In reverse, Harry, Ron and Hermione could end up in Arendelle. Hermione might be intrigued by the way Elsa controls her ice powers and try to find a scientific or magical explanation for it. Also, the Dementors from Harry Potter could be compared to the dark forces in Frozen 2, like the mist that Elsa has to face.
One interesting crossover could be the use of magic in the Avengers world. For example, Hermione could use her knowledge of spells to help the Avengers solve a problem that technology couldn't. Maybe she could use a spell to break through an impenetrable force field created by an enemy. Another aspect could be the Avengers characters learning magic. Tony Stark might be fascinated by the concept of magic and try to incorporate it into his technology. Or Thor could share his knowledge of Asgardian magic with the Hogwarts students.
One interesting crossover could be a scenario where Hermione uses her magic to help Elsa control her powers better. Maybe she creates a spell that can soothe Elsa when she's about to lose control.
In some fanfiction, Maleficent might team up with a dark wizard from the Harry Potter universe. They could combine their powers to try and take over both the wizarding world and the fairy - tale land where Maleficent comes from. This would create a complex power struggle with the heroes having to find new ways to combat them.
One interesting crossover could be the characters from Harry Potter visiting Narnia. For example, Harry, Ron, and Hermione might find themselves in Narnia through some magical accident. They could then interact with the talking animals and magical beings there, like how they interact with the magical creatures in their own wizarding world. Maybe they would help the Narnians in a battle, using their unique Hogwarts - taught magic.
One interesting crossover could be the use of spells. For example, a Charmed one might learn a spell from the Harry Potter world like the Patronus charm. It could be used in a new and different way in the Charmed universe, perhaps to fight a new type of demon that is vulnerable to positive magic like a Patronus.