Another idea is a crossover where the villains from both universes team up. Voldemort and the League of Villains could form an alliance. This would force the heroes from My Hero Academia and the students at Hogwarts to work together. They would need to combine their magical and quirk - based powers to defeat this powerful evil force.
One idea could be that Hulk somehow gets transported into the wizarding world of Harry Potter. Maybe a magical experiment gone wrong by a Hogwarts student creates a portal that sucks Hulk in. He could then cause chaos as he's not used to the magic and strange creatures there.
One idea could be a story where a Wendigo somehow enters the wizarding world of Harry Potter. Maybe it's brought in by a dark wizard who wants to use it as a weapon. The Trio - Harry, Ron, and Hermione - would then have to figure out how to defeat it using their magic and knowledge.
Another possibility is that Voldemort creates a spell that combines the dark elements of his magic with the curse from Beauty and the Beast. The Trio then has to find a way to reverse it. They might discover that the solution lies in the same kind of selfless love that breaks the Beauty and the Beast curse. This could lead to some really interesting character development and plot twists.
One idea could be that the Space Captain crash - lands on the magical world of Harry Potter. He has to learn about magic to repair his ship while Harry and his friends are intrigued by the advanced technology the captain brings. Maybe they team up to fight a new threat that is endangering both the wizarding world and the space captain's galaxy.
A more complex fanfic could involve a dark wizard from the Harry Potter world trying to use the power of the music and the happy atmosphere in Mamma Mia as a way to hide from the Aurors. The characters from Mamma Mia would initially be unaware of the danger but gradually team up with the Harry Potter crew to defeat the dark wizard. This would combine the magic of Harry Potter with the sunny, carefree setting of Mamma Mia.
One idea could be a crossover where Harry Potter characters end up in the world of Prince of Tennis. For example, Harry could befriend some of the tennis players and learn about their passion for the sport. Maybe he could even try his hand at tennis, using his magic to add some unique twists to the game.
A third fanfic concept could involve a character from the Harry Potter series stumbling into Alma Wade's world. Let's say Hermione accidentally discovers a portal that leads to Alma's realm. She has to use her knowledge of magic and her wits to survive in this strange new place. Meanwhile, Alma Wade is intrigued by Hermione's magic and they start to learn from each other, with Hermione introducing wizarding spells and Alma sharing her unique powers.
A story could be about a character from the Harry Potter universe who gains superhero - like abilities and then discovers she's pregnant. This could lead to a whole new set of adventures as she tries to protect her unborn child and the wizarding world. For example, she might have to use her new powers in unexpected ways to fend off dark wizards while being pregnant.
Another possibility is a story set in a world where the Mortal Kombat realm and the Harry Potter universe have merged. Cassie Cage, being a fighter from Mortal Kombat, could be teaching the Hogwarts students some self - defense moves. In return, the students could teach her about magic. This would lead to a lot of interesting interactions, especially when it comes to handling different kinds of threats in this new merged world.
One idea could be that the Addams family somehow ends up in the wizarding world of Harry Potter. Maybe Wednesday Addams could be a transfer student to Hogwarts. She would be really unique among the students, with her strange interests and dark sense of humor. She might not be too impressed with the magic at Hogwarts as she has her own 'creepy' ways of doing things at home.