One interesting crossover could be a situation where Jack Sparrow stumbles upon Hogwarts. Maybe he's looking for some magical treasure hidden there. He'd be completely out of place among the wizards and witches, and his roguish ways would likely cause all sorts of chaos and confusion.
Another aspect could be the cultural clash. Jack Sparrow comes from a world of pirates, with their own set of rules and values, while Hogwarts has its own complex system of magic and morality. In fanfiction, this clash can be explored in depth. For example, Jack might not understand the concept of not using dark magic, thinking that any magic that gets the job done is fair game. This could lead to some tense moments between him and the more morally upright characters in the Harry Potter universe, and also open up opportunities for character growth and change as they learn from each other.
A crossover could also involve a magical object from the Harry Potter universe being related to the Jack the Ripper case. Maybe the Ripper was after a powerful magical relic that was hidden in muggle London. Harry and his friends would then have to find the relic before the Ripper does, to prevent him from using its power for evil purposes.
Well, it's not a traditional or common concept. Fanfiction usually involves playing within the boundaries of a single fictional universe or at least related ones. Harry Potter has its own set of rules, characters, and storylines, and the same goes for Jack Sparrow's world. However, in the realm of fan creativity, anything can be possible. Maybe someone could write a story where Harry Potter is a big fan of the tales of Jack Sparrow and tries to incorporate some pirate - like adventures into his magical quests.
One interesting crossover could be the use of Avatar's bending abilities in the wizarding world of Harry Potter. For example, a character who can bend water could use it to create unique defenses against dark magic spells that involve fire. Another could be the idea of Hogwarts having an exchange program with the Avatar world, and students from each side learning about the other's culture and magic systems.
One interesting crossover could be the use of magic spells from Harry Potter in the Skyrim world. For example, the 'Expelliarmus' spell might be used to disarm an enemy in Skyrim instead of the normal combat disarming moves. Another could be the appearance of Hogwarts-like structures in Skyrim. Wizards from Harry Potter might also find their way into Skyrim and interact with the local mages there.
A really cool concept in this type of fanfiction is when the magic items from both universes interact. Like, what if the Philosopher's Stone was brought to Narnia? How would it affect the balance of magic in Narnia? And how would the Narnians react to such a powerful and mysterious object?
One interesting crossover could be the magic system of Harry Potter combined with the ninja skills in Naruto. For example, a story where Naruto characters learn to use wands and spells while Hogwarts students learn chakra control. Another could be a plot where Voldemort teams up with Orochimaru to take over both the wizarding world and the ninja world. There could also be a story about Harry Potter being reincarnated as a ninja in the Naruto world and using his knowledge of magic in new and unexpected ways.
One interesting crossover could be the use of ninjutsu in the wizarding world. For example, Naruto's shadow clone jutsu could be used by a Hogwarts student to attend multiple classes at once, leading to all sorts of comical and chaotic situations in the hallways of Hogwarts.
One interesting crossover could be the idea of Hogwarts students having mutant abilities. For example, a student who can control the weather like Storm from X - Men. It would create a whole new dynamic within the Hogwarts environment, with new challenges and friendships.
One interesting crossover could be the magic system of Harry Potter being introduced to the MHA world. For example, a character from MHA might discover they have magical abilities like a Hogwarts student. Another could be the heroes from MHA having to face off against dark wizards from the Harry Potter universe. It would be a really cool mix of the two different power dynamics.
Another crossover could be in the form of a quest. Imagine a Reborn character joining Harry, Ron and Hermione on their search for Horcruxes. Their different skillsets would make for an interesting combination. The Reborn character might have knowledge or abilities that help the trio avoid danger more easily or even discover new Horcruxes that were previously hidden due to their unique perspective.