One way it could work is if there was a prophecy in both worlds that foretold of a hero from each realm coming together. Harry Potter, being the hero of the wizarding world, and Aquaman, the hero of Atlantis, are brought together by this prophecy. They start off not trusting each other, as they are so different. But as they face challenges together, like sea monsters attacking the coast near Hogwarts or dark wizards trying to steal treasures from Atlantis, they learn to respect and rely on each other, and their combined efforts save both worlds.
One common theme is the clash of two different worlds. The underwater world of Aquaman and the magical world of Harry Potter are very different, so seeing how they interact, like the cultural differences between muggles and Atlanteans, is often explored.
One possible plot could be that Aquaman somehow finds himself in the wizarding world of Harry Potter. Maybe a magical spell gone wrong transports him there. He could use his unique underwater abilities to help the Hogwarts students in a task related to the Black Lake, like retrieving a powerful magical artifact that has sunk to the bottom.
It could be really interesting. Maybe Aquaman could visit Hogwarts and interact with the students. He might be amazed by the magic there, like the floating candles in the Great Hall. And perhaps he could teach the wizards about the underwater world of Atlantis, introducing them to mermaids and sea creatures they've never seen before.
Well, in a 'Harry Potter son of Aquaman' fanfiction, the story could start with Harry being an outcast at Hogwarts because of his strange connection to the ocean. As he grows older, he realizes he can control water in ways other wizards can't. This leads to him being both feared and admired. He could then go on a quest to find out more about his father Aquaman and in the process, use his combined magical and Aquaman - like powers to defeat a dark force that threatens both the wizarding world and the underwater kingdom.
One possible plot could be that Harry Potter discovers a magical portal that leads him to the underwater world of Aquaman. There, he has to learn the ways of the underwater society while also using his magic to help Aquaman fight against an evil force that threatens both the wizarding world and the underwater realm. Maybe a dark wizard has teamed up with a sea - based villain, and Harry's unique skills are needed to defeat them.
One great Aquaman Harry Potter fanfiction is 'The Wizard of the Deep'. It combines the magical world of Harry Potter with the underwater realm of Aquaman in a really interesting way. The characters from both universes interact in a believable manner, and the plot is full of twists and turns.
Well, in a Harry Potter and Aquaman crossover fanfiction, we might see Aquaman's Atlantean magic interacting with Hogwarts' magic. For instance, the Sorting Hat might have a hard time sorting an Atlantean student brought by Aquaman. Also, Harry and his friends could go on an adventure to Atlantis with Aquaman as their guide, exploring the underwater world full of strange creatures and ancient magic.
The main antagonist could be a dark wizard who has mastered water - based magic and has made a pact with a powerful sea monster. This dark wizard wants to rule both the wizarding world and the underwater world. He sees Harry Potter as a threat to his plans in the wizarding world and Aquaman as a hindrance in the underwater realm.
Finding such a specific fanfiction can be a bit of a challenge. You could start by looking on major fanfiction websites like Archive of Our Own or FanFiction.net. Use their search functions and type in relevant keywords like 'Mera', 'Aquaman', 'Harry Potter' and something indicating a crossover. But there's no guarantee it exists or that you'll be able to find it easily.
Aquaman's ability to control the sea could be used to create massive water - based defenses around Hogwarts. In return, Harry could use magic to give Aquaman the ability to breathe air indefinitely when he's on land for extended periods. Their powers could also combine in a more offensive way. For instance, Harry could use a levitation spell on Aquaman while he's in the water, allowing Aquaman to attack enemies from above the water surface with his enhanced speed and strength.