Perhaps the magic in the alternate universe functions in a distinct way. Harry might discover new spells or magical abilities that don't exist in his own universe. He could also find that some of the magical creatures he is familiar with have evolved into very different forms or have different roles in the alternate wizarding society.
In the alternate universe, Harry could meet different versions of his friends and enemies. His relationship with them would be very different. For instance, Hermione might be a Death Eater or Ron could be a powerful dark wizard. It would be a huge shock for Harry to deal with these new identities of people he thought he knew well.
If Harry Potter goes to the DC Universe in a fanfiction, it could be really interesting. His magical skills would be a new element in the DC world. He might be confused by the different powers and technologies there. For example, his invisibility cloak would be a different kind of 'invisibility' compared to the technology - based ones in DC. He could also learn a lot from the DC heroes about courage and justice, and in turn, teach them about the magic world.
Ash could become a powerful villain in the alternate universe fanfiction. Maybe he has a different backstory that led him to the dark side.
Well, Harry could be really confused at first. Ouran is a very different world from Hogwarts. He might be shocked by the opulence of Ouran Academy and the strange club system there. Maybe he'd try to find a way to fit in while still being true to his wizard self.
Maybe Harry has some strange magical illness that normal wizards can't cure. So he has to seek help from a very special doctor who might have some unique remedies.
Perhaps he would be seen as an oddity at Alfea. After all, he comes from a completely different magical system. But his reputation as the 'Boy Who Lived' might precede him. Some might be in awe of him, while others might be skeptical. His presence could also stir up some rivalries among the students at Alfea who are used to their own hierarchies. Harry would have to find his place among the fairies and deal with any potential jealousies or hostilities.
Well, he might encounter new magical creatures unique to America, like the Thunderbird. He could also visit American wizarding schools and be amazed by their different teaching methods compared to Hogwarts.
In this fanfiction, Harry could attend a Canadian wizarding school. He'd have to adapt to a different teaching style and make new friends. The curriculum might include courses on Canadian magical history and spells that are specific to the region. He might also face some challenges from local wizards who are not used to having a famous wizard like him around.
Well, in this fanfiction, Harry Potter might face new magical challenges in the ICW (International Confederation of Wizards). He could encounter different magical cultures and spells from around the world. Maybe he'll make new friends or enemies among international wizards.
Well, he might visit Beauxbatons Academy. Maybe he would meet some new friends there, like some interesting French wizards or witches. He could also explore the French wizarding culture, which is likely different from what he's used to in England.
His Gryffindor courage would still be put to the test. There could be difficult exams and challenges at college. He might also get involved in some sort of college - wide magical competition. And he would have to balance his social life, his studies, and any potential threats from the dark magic side that still exists.