Voldemort could be the most interesting character in this fanfiction. We usually see him as a purely evil character. But as a partner to Harry, we might get to see a different side of him. Maybe there are some remnants of his humanity that start to surface. His transformation from an all - out villain to a reluctant partner would be a fascinating character arc.
I think Harry would be the most interesting. He has always been the hero who stands against Voldemort. But now as partners, he has to deal with his own internal conflict of teaming up with his arch - enemy. His struggle to balance his moral values with the need to work with Voldemort would be really engaging to read about.
One possible plot could be that they are forced to be partners to save the wizarding world from an even greater threat. Maybe an ancient evil that neither of them can face alone. So, they have to put aside their differences and work together, which would be a huge change from their usual enmity.
I think Voldemort would be the most interesting. We rarely get to see his perspective in the original series. In a fanfic where Harry talks to him, we might get to see a more complex side of Voldemort. Maybe he'll show some vulnerability or a different motivation than just pure evil. It could be really fascinating to see how he reacts to Harry's words and if he is capable of any change.
Harry Potter himself would be very interesting. Combining his wizarding skills with Kryptonian powers would make him an extremely powerful character. He could be the bridge between the two worlds and use his new powers to protect both the wizarding world and the world of Kryptonians on Earth.
Snape and Madarao would be an unexpected but fascinating pairing. Snape's brooding and complex personality could interact in an interesting way with Madarao's more straightforward and loyal nature. Snape could perhaps study the unique yokai magic associated with Madarao, and Madarao could be both amused and intrigued by Snape's potions and spells.
Definitely Harry Potter and Rias. Rias is used to leading and being in control, but Harry has his own strong sense of justice and leadership. Their interactions could be full of power plays and mutual respect as they try to figure out how to work together.
It could be Aquaman. He is so different from the wizards in the Harry Potter universe. His fish - like abilities and his role as a king would make for some great interactions with the Hogwarts students and professors. He could teach them about the ocean and its secrets, while also being amazed by the magic of wands and potions.
Percy would be really interesting. His ability to control water and his laid - back yet brave personality would contrast well with the more formal wizarding world. He could make some really funny and unexpected interactions with the Hogwarts students and teachers.
I think Hermione would be really interesting. She's already very intelligent and resourceful. If she got the Venom symbiote, she could use its powers to access areas that are normally restricted in the wizarding world, like the restricted section of the library, and find new spells and knowledge. She could also use the symbiote's physical abilities to protect her friends during dangerous situations.
I think Harry Potter and Nick Burkhardt would be an interesting pairing. Harry has his experience with fighting dark magic and Nick has his knowledge of the Wesen world. They could learn a lot from each other. Harry could teach Nick about some of the more complex spells, while Nick could introduce Harry to the different types of Wesen and how to deal with them.
I think their first - born child would be really interesting. This character would have the combined traits of Harry and Hermione. They'd have Harry's natural leadership and Hermione's thirst for knowledge. Just imagine this kid growing up, trying to live up to their parents' legacies while also forging their own path in the wizarding world.