Harry's magic could fit in an interesting way. In ancient Greece, there were already ideas of magic and the supernatural. His magic could be seen as an advanced form of what they knew. For example, his ability to apparate could be like a super - fast form of travel that the Greeks might have only dreamed of. His magic could also disrupt the existing power structures. If he was on the side of the common people, the powerful rulers and priests might see him as a threat. On the other hand, if he worked with them, he could become a very influential figure. He could also use his magic to help in the construction of great buildings or to preserve ancient knowledge that was in danger of being lost.
His magic would likely be seen as a great power. The Greeks might think he was a demigod or had some divine connection. His spells could be used for various things like protecting villages from monsters or helping with crops.
Zatanna's magic, which often involves speaking spells backwards, could be seen as a very unique form of magic in the Harry Potter universe. It might be initially misunderstood by the Hogwarts students and teachers. But as they learn more about it, they could find ways to incorporate it into their own magical studies. For example, it could inspire new ways of casting defensive spells.
Well, it might be hidden at first. Since the Winchester world is more about physical combat and hunting non - magical threats, Harry might have to keep his magic a secret. He could use it in a very discreet way when it's absolutely necessary, like when facing a magical creature that normal Winchester methods can't handle.
His magic might be more elemental. Since Greek magic often ties in with the elements like fire, water, earth, and air. He could have an easier time with spells related to these elements compared to other Hogwarts students.
It would be a very difficult fit. Since the wizarding world has its own norms like monogamous relationships in most cases (like the marriages we see in the series). If one were to introduce concubines, it would have to be in an alternate universe where the social and moral values are completely different. Maybe in a fanfic where the wizarding world is modeled after a more ancient and permissive society, but this would be a huge departure from the original feel of the Potterverse.
Mileena could be a foreign exchange student of sorts from a different magical realm. Her unique appearance and combat skills would make her stand out at Hogwarts. She might have trouble adjusting to the more academic and rule - based magic of the wizarding world compared to her own more instinctive and combat - focused magic.
He'd fit in by sharing his magic skills. His ability to perform spells without using hand gestures (unlike most Fairy Tail mages) would be a novelty. He could also bond with the other members over their love for magic.
He could fit in as a unique hero. His magic could be seen as a special power like the others in DC. For instance, he could use his Patronus charm to fight off fear - inducing villains.
Alucard could be a part of an ancient prophecy in the Harry Potter fanfiction. His arrival in the wizarding world could be foretold. He might be seen as a savior or a bringer of chaos. His powers could be seen as a necessary evil to defeat a greater threat, like a new and more powerful form of Voldemort. He would bring his own brand of violence and mystery to the relatively more structured world of Harry Potter, making for a very exciting and unpredictable story.
One way is through power sharing. If Harry's soulmate is an Avenger, they could combine their powers. For instance, if it's Iron Man, they could use magic to enhance the technology. Magic could be used to make the suit more powerful or give it new abilities like cloaking. The soulmate bond would make them work in harmony, understanding each other's strengths and weaknesses.
Hawkgirl could be a new kind of magical creature. Her ability to fly with her wings would be a unique form of magic in the wizarding world. She might be a protector of some hidden magical place in Hogwarts or the Forbidden Forest, like a guardian of an ancient magic that Voldemort is after.