Hades himself would be a central character. His influence on Mal, his parenting style, and his own motives for raising Mal would be important aspects of the story.
Depending on how the fanfiction is written, characters like Maleficent could also play a role. Maybe she tries to reclaim Mal from Hades, or there could be some sort of power struggle between them over Mal's future.
One interesting idea could be Mal's unique powers evolving in a different way under Hades' influence. For example, her magic might take on a darker or more underworld - themed aspect.
Harry for sure. Then there could be his samurai mentors. Maybe there would also be some characters from the original Harry Potter world who interact with him in this new samurai - influenced life. For example, Hermione might visit him in the samurai village and be amazed at the new skills he has learned.
Well, Harry is the central figure in this fanfiction idea. Since he is being raised by Hidan, Hidan becomes a crucial character too. Then, there could be characters like Hermione. She might be either very intrigued or very concerned about Harry's new upbringing. And of course, there could be antagonists from both universes. In the Harry Potter world, Voldemort or his followers could still be a threat, and in Hidan's world, there might be some enemies that could cross over into Harry's life in this fanfiction.
Obviously, Ash and Arceus are the main characters. Ash is the one being raised, and Arceus is the one doing the raising. But there could also be other Pokémon that are important in Ash's upbringing, like the Pokémon that Arceus assigns to look after Ash or be his companions during his growth.
Naruto and Sheogorath are the two most likely main characters. But there could also be appearances from some of Naruto's original friends like Sasuke and Sakura, though their relationships with Naruto would be very different. They might be more like outsiders looking in on Naruto's strange new life under Sheogorath's influence. Also, characters from the Sheogorath's world might make an appearance in the fanfiction, further complicating Naruto's life and the overall story.
Obviously, Naruto and Alduin would be the main characters. Naruto is the one being raised, so his growth and development under Alduin's influence would be central. Alduin, on the other hand, is the one doing the raising. His motives, his power, and his relationship with Naruto would be key aspects of the story.
Obviously, Percy would be one of the main characters. Chaos, who raises him, would also be very important. There might also be some other primordial beings that interact with Percy during his upbringing.
Obviously, Percy and Hades will interact a great deal. Percy will also likely interact with the Furies, as they are servants of Hades. They could be like his protectors or trainers in some sense. Another character could be Nico di Angelo, since he has a connection to Hades as well. They could bond over their shared relation to Hades.
Obviously, Naruto and Erza would interact a great deal. Naruto would also probably interact with Erza's friends from Fairy Tail. He might meet Natsu and they could have some interesting battles or friendly competitions. He could also interact with Lucy, and perhaps learn about celestial spirits from her.
Well, Harry Potter is the central figure, but the Weasley siblings are key too. Fred and George could be like his fun - loving older brothers, teaching him all kinds of mischievous spells and pranks. Ginny would be like a sister, and their relationship could develop in a really interesting way. And Percy, despite his differences from the rest of the family, would also be an important character as Harry would be part of the family dynamic that Percy is also a part of.