Definitely Doctor Strange. He already has a deep understanding of magic in the Avengers universe. In the Harry Potter world, he could exchange knowledge with the wizards, learn new spells, and maybe even help improve the defenses of Hogwarts. He could also have some really cool battles against the dark wizards using his unique combination of magic and martial arts.
Captain America would be an interesting choice. His strong sense of justice and leadership would be a great addition to the Harry Potter world. He could inspire the students at Hogwarts to stand up against the dark forces, and his combat skills would be useful in fighting the Death Eaters. Plus, it would be fun to see him interact with the magical creatures and try to understand the wizarding culture.
I think Gandalf would be a very interesting character to cross over. He has so much wisdom and power in LOTR. In the Harry Potter world, he could share his knowledge of different magics and perhaps help Dumbledore in his fight against Voldemort. He could also introduce the concept of the greater good in a more profound way to the young wizards and witches.
Hermione Granger would be really interesting. She could bring her intelligence and magic skills to the OITNB world. She might start a library or a study group for the inmates, teaching them about magic and also helping them with their own educational pursuits. Her strong - willed and determined nature would make her a force to be reckoned with in the prison environment.
Definitely Doctor Octopus. Imagine him getting his hands on some magic wands and using his mechanical arms to perform complex spells. He could be a really formidable villain in the wizarding world, and it would be exciting to see how Harry Potter and Spiderman would team up to stop him.
Hermione is a prime candidate for an interesting crossover. In an anime world like My Hero Academia, she could use her intelligence and magic to attend U.A. High School. She'd be a unique student, using spells instead of quirks, and could help solve some of the complex problems in that world. Ron Weasley could also be fun. If he crossed over into the world of Inuyasha, he could bring his sense of humor and his skills with magic items. He might accidentally cause some chaos with his clumsy ways, but also be a valuable ally in the fight against Naraku. And then there's Luna Lovegood. In an anime like Spirited Away, her dreamy and eccentric nature could fit right in as she explores the strange spirit world, using her unique magic and knowledge of the wizarding world's odd creatures.
Dumbledore and Galadriel. Both are very powerful and wise characters. Dumbledore with his deep understanding of magic and his ability to see the good in people, and Galadriel with her elven magic and her role as a protector. Their encounter could lead to some very interesting discussions about the nature of magic, good and evil, and how to deal with powerful dark forces in both their worlds.
Dumbledore could be an amazing crossover character. His vast wisdom and powerful magic would make him a force to be reckoned with in the Overlord world. He could potentially see the good in some of the 'evil' characters and try to guide them towards a better path. His presence would also shake up the power balance in the Overlord world as different factions would either fear or seek to ally with him.
Definitely Harry Potter and Luke Skywalker. They both are heroes on a journey to defeat great evils. They could learn from each other's experiences and powers. Harry could show Luke some of the more subtle forms of magic, and Luke could teach Harry about the Force.
I think Jack Sparrow from 'Pirates of the Caribbean' would be really cool to cross over with Hercules. Jack's wily and unpredictable nature would contrast with Hercules' more straightforward heroism. They could be on a quest for a magical artifact that has the power to either save or destroy the world. It would be full of adventure, humor, and unexpected twists.
Dumbledore could be an extremely interesting crossover character. His wisdom and powerful magic would make him a force to be reckoned with in the Kantai Collection world. He could potentially teach the shipgirls about different forms of magic, and his ability to see the bigger picture would be useful in strategizing against the Abyssal threats.
Joker from the Phantom Thieves would be really interesting. He has a mysterious and complex personality. If he were to cross over into the Death Note world, his skills in manipulating situations and people could put him in direct conflict with Light. He might be able to outwit Light in ways that others couldn't, and his sense of justice, which is more about reforming society on a personal level, would contrast greatly with Light's more extreme views.