One way the storylines could blend is through a magical event that transports Harry Potter characters to the DC universe where they meet Martians. Maybe a spell gone wrong by Hermione accidentally opens a portal. The Martians, with their unique abilities like telepathy, could interact with the wizards. For example, J'onn J'onzz could communicate with Dumbledore using his telepathy and they could team up against a common enemy like Voldemort who has somehow made his way into the DC universe as well.
Harry Potter and Superman would have an interesting interaction. Superman's super strength and invulnerability might be a source of wonder for Harry, while Superman could be intrigued by the magic Harry wields. Martians, like J'onn J'onzz, could interact with both. J'onn could use his shape - shifting ability to blend in at Hogwarts and learn about magic, and also team up with Superman to face any threats that cross over from the wizarding world.
One common theme is the clash of different power systems. In Harry Potter, there's magic, and in DC, there are super - powers. Fanfictions often explore how these two types of powers interact, whether they complement each other or cause conflict.
It could be really exciting. Maybe Harry Potter characters could visit Gotham City. Harry could use his magic to help Batman fight crime in a way that normal gadgets can't. For example, he could use spells to disarm villains from a distance or create magical barriers to protect civilians.
One idea could be that Harry Potter and his friends are transported to the DC Comics universe. They could team up with the Justice League to fight a common enemy like Voldemort who has somehow gained powers from a DC Comics villain. For example, Voldemort could have made a deal with Darkseid to gain more power in exchange for helping him conquer the wizarding world first. Then, Harry and the likes of Superman, Batman, and Wonder Woman would have to combine their magical and super powers to stop them.
There's 'Magic and Metahumans'. This fanfiction has a great plot where the Death Eaters from Harry Potter somehow end up in Metropolis. Superman has to deal with their dark magic while Harry and his friends try to find a way back to their world. It's full of action and interesting character dynamics.
There's a story on AO3 where Batman visits Hogwarts to investigate some strange disappearances. What makes it stand out is how well the author captures Batman's detective skills in the magical setting. He's able to use his gadgets and his wits to figure out that a Slytherin student is using a dark magic spell that's related to a DC Comics - style super - power experiment gone wrong. It's a complex and engaging plot.
One great one is 'The Wizard and the Caped Crusader'. It combines the magic of Harry Potter's world with the superhero action of DC. It has a really interesting plot where Harry somehow ends up in Gotham City and has to team up with Batman to fight a new kind of dark magic that's threatening both worlds. Another is 'Magic in Metropolis' which shows Superman dealing with the sudden appearance of Hogwarts students in his city. They bring chaos at first but then they all work together to face a common enemy. There's also 'Potter and the Justice League' which features Harry joining forces with the entire Justice League to take on Voldemort who has made an alliance with some of DC's villains.
I think Darkseid would be the most unexpected. Imagine Harry Potter being raised in Apokolips. He would have to adapt his magic to survive in such a harsh and evil - dominated place. His magic could potentially be a threat to Darkseid's rule, or he could learn some dark magic - like powers from Darkseid's regime, which would completely change his character and the way he uses magic.
Well, in a 'Harry Potter raised DC crossover fanfiction', perhaps Harry is raised by Wonder Woman. He could grow up learning about Amazonian values along with his own magical heritage. His magic might be seen as a new form of power in the DC world. For example, he could use magic to create protective shields during battles against the forces of Ares. Or he could be raised by the Flash, and use his magic to help the Flash with time - related problems, like creating a time - freezing spell to stop a time - traveling villain.