Well, one possibility is that Harry could use his magic skills to fight the crime in Gotham. He might team up with Batman, with Harry using spells like 'Expelliarmus' to disarm criminals while Batman does his stealthy thing. Maybe Harry would be initially confused by Gotham's dark and gritty atmosphere compared to Hogwarts.
The plot could involve Harry trying to keep his magic a secret in Gotham. He could end up in Arkham Asylum by mistake and have to use his magic to escape the crazed inmates. And then he'd start to realize that Gotham has its own kind of 'dark magic' in the form of the villains like the Joker, and he'd try to combat that with his own brand of magic and heroism.
Perhaps Harry would attend a regular school in Gotham while secretly using magic to help those in need. He might befriend some of the younger characters in Gotham, like Robin. And as he gets more involved in Gotham's affairs, he'd find that his Hogwarts training has prepared him in ways he didn't expect for the challenges of this new and dangerous city.
Scarecrow could also be a main antagonist. His fear - inducing toxins could be a real problem for Harry. Harry would have to use his magic to counter the effects of the fear toxin and also figure out a way to stop Scarecrow from spreading it all over Gotham.
Well, perhaps Harry Potter arrives in Gotham City and is appalled by the state of it. He decides to adopt some of the children who are in difficult situations. As he does this, he uses his Hogwarts education and magical skills to protect them from the likes of the Penguin and other villains. He might even introduce some magic into Gotham's society in a very subtle way, like using spells to improve the living conditions in the slums where he and the adopted kids live.
Well, perhaps Harry moves in with McGonagall because Hogwarts has been damaged and he has no other place to go. McGonagall could then take on a more motherly role, teaching Harry advanced magic and helping him deal with his PTSD from all the battles.
Well, in this fanfiction, Harry could move to America to escape the fame and the dark memories in the UK. In America, he might find a more laid - back wizarding community. He could start a new life working in a small magic shop in a wizarding town. There, he meets a group of young American wizards who are trying to fight against a new dark force emerging in the States. Harry then uses his skills and experiences from Hogwarts to help them out.
Maybe Harry moves to Canada to escape the wizarding world chaos in Britain. He could start a new life, perhaps teaching magic secretly in a small Canadian town.
One possibility is that Harry, with his magical skills, could introduce a whole new type of magic to Konoha. Maybe he'd help the ninjas with some of their toughest problems using spells like 'Accio' to retrieve lost items during missions. He could also learn about chakra and combine it with his magic in unexpected ways.
One possibility is that Harry discovers a new magical community in California. Maybe there are different types of magic there compared to what he knew in the UK. He could meet new friends who have a unique understanding of magic based on their Californian upbringing.
Well, perhaps Harry Potter would use his magic in Metropolis in unexpected ways. He might help Superman with some magical threats that his superpowers can't handle. For example, a villain using dark magic to create illusions across the city.
In this fanfiction, Harry could be on a quest related to some ancient magic that is tied to New Orleans. He may end up getting involved with the local magical community's power struggles. For example, there could be a fight over a powerful voodoo talisman, and Harry's skills from his Hogwarts days come in handy to help resolve the situation. Also, he might start to learn about the unique magical creatures that are native to the area.
One possible plot could be that Fem Harry Potter, let's call her Harriet, moves to America to attend a special magical school there. She might face challenges in adapting to the different magical culture. For example, the way spells are taught or the social hierarchy among American wizards could be very different from what she's used to in Hogwarts. Maybe she'll make new friends who introduce her to unique American magical creatures and spells.