There could be some sort of primordial council or group of elders in this fanfic. They would be the ones who have knowledge about the primordials and their descendants. Harry would interact with them, and they could either be his allies or his antagonists. Then there are the regular students at Hogwarts. Some might be jealous of Harry's new powers, while others might be in awe. And we can't forget about the magical creatures, like centaurs or house - elves, who might also have a different view of Harry due to his primordial connection.
Obviously, Harry himself as the son of Atlas. Then there could be the original characters like Dumbledore, who might play a role in guiding Harry about his new identity. Hermione would still be there, probably helping Harry research about Atlas. And Ron, as Harry's friend, would be involved in his adventures.
Obviously, Harry Potter himself. Then there could be the dragons, perhaps an old and wise dragon that acts as Harry's mentor. Hagrid might also play an important role as he has a connection with magical creatures and could help Harry understand his new identity.
Well, it might involve Harry having powers far beyond what was shown in the original series. Maybe he could control primordial elements like fire, water, earth, and air in a more extreme way. He could also have a different kind of connection to the magical world, perhaps being able to communicate with ancient magical beings related to the primordials.
Obviously, Harry Potter himself as the main character. Then there would be the members of the Black family, like Bellatrix Lestrange who could have a different attitude towards Harry. And of course, Sirius Black would play a different role as Harry's family member.
Hermione would definitely be there. She would be intrigued by Harry's new heritage and would probably try to research all about Ra in the Hogwarts library. Ron too, would be by Harry's side, though he might be a bit more skeptical at first about this whole Ra business.
In this fanfiction, Voldemort could also be involved in a different way. Since Harry is now the son of the Demon King, Voldemort might see him as a threat or a potential ally. Dumbledore would surely play a role too. He might be the one to guide Harry or try to keep him from fully embracing his demonic side. And there could be some magical creatures that are associated with the demonic realm, like imps or minor demons that could be characters in their own right.
A new young teacher at Hogwarts. She could be a prodigy in Transfiguration, having mastered some really advanced spells at a young age. She brings a fresh perspective to teaching and has a bit of a rivalry with McGonagall in the fanfic. She might also have a mysterious past that is gradually revealed throughout the story.
Obviously, Madam Pomfrey is a key character as she runs the hospital wing. Harry, Ron, and Hermione could also be characters, perhaps they visit a friend who is ill. There could also be some minor characters like Neville who might get injured during a Herbology class and end up in the hospital wing.
Obviously, Harry Potter himself. Then there could be some Canadian - born witches and wizards as his friends. Maybe a tough - as - nails girl from the Yukon who is an expert at ice magic. And a laid - back boy from Vancouver who has a special talent for communicating with magical forest animals.
Obviously, Harry Potter himself. There could also be some Beautox - natives, like a wizard or witch who is an expert in Beautox magic. Maybe Hermione would somehow find a way to follow Harry and she'd be there too, trying to figure out the new magic system.