Theodore Nott could be an interesting character to interact with Harry. He is a relatively quiet Slytherin in the original books, but in the fanfiction, he might open up more to Harry. And of course, the other Slytherin students as a whole. Harry would have to deal with the general Slytherin attitude towards him, which could be a mix of suspicion, envy, and some level of admiration as he is the famous Harry Potter.
Snape would have a very different relationship with Harry in this scenario. Instead of being a constant source of disdain, he might see Harry as an opportunity to shape a Slytherin in a new way. Pansy Parkinson could also be involved. She might initially be against Harry being in Slytherin but later come to accept him, or they could be in a constant battle of wits.
Obviously Gibbs himself would be a main character interacting with Harry. He'd be like a father figure.
The main characters in 'Harry Potter raised by Winchesters' fanfiction would have some interesting interactions. Harry would surely have a lot of interaction with the Winchesters' enemies as well. Demons and other supernatural beings that the Winchesters fight would see Harry as a new target or a strange addition to the mix. In the wizarding world, Harry might interact with Snape in a more confrontational way, as his upbringing by the Winchesters could make him less patient with Snape's attitude. Also, new characters from the cross - over of the two universes could be created, and Harry would be at the center of those interactions.
I think Harry Potter would definitely cross paths with Tyrion Lannister. Tyrion is known for his intelligence and wit, and Harry's unique perspective from the wizarding world could lead to some great conversations and schemes between them. Harry could also use his magic to help Tyrion in his political struggles within Westeros.
Obviously, Harry would interact a great deal with Newt. But also, they might run into other characters like Hagrid. Hagrid, being the Keeper of Keys and Grounds at Hogwarts and having a great love for magical creatures, would be interested in what Newt and Harry are up to. They could also meet some of Newt's old friends from his adventures in the Fantastic Beasts series.
Voldemort would be a likely character to interact with Harry. Since Bellatrix was one of Voldemort's most loyal followers, he might take an interest in Harry as her son. He could either see Harry as a potential powerful ally or a threat depending on how his powers develop. Another character could be Draco Malfoy. Given the connection between the Malfoy family and the Death Eaters, Draco might have a complex relationship with Harry, perhaps initially seeing him as an equal in the dark magic world but later having doubts as Harry shows signs of not fully embracing the dark side.
Hermione and Betty would be likely to interact. Hermione's intelligence and thirst for knowledge could pair well with Betty's investigative nature. They could work together to solve a mystery that spans both the wizarding world and Riverdale.
Neville could be another character. He might look up to Harry even more in his dragon form, seeing him as an even more powerful protector. Hagrid would be excited to have a dragon - Harry around. He could help Harry understand his new dragon nature. And some of the Slytherins, like Draco, might be jealous or scared of Harry's new form.
Obviously, Harry Potter himself is the central character. His journey in Slytherin would be the main focus.
The Slytherin Prince is, of course, central. Then there might be characters like Draco Malfoy, who could be either a friend or a rival to the Slytherin Prince. Hermione Granger could also be involved, as she often crosses paths with different characters in fanfictions. Additionally, there could be original characters created specifically for this fanfiction, perhaps a long - lost relative of the Slytherin Prince who has some secrets to share.
Hermione would probably be one of the main characters to interact. She might be horrified at first to see Harry in such a situation and would try to find a way to free him. Ron could also be involved, perhaps being more impulsive in his attempts to rescue Harry, which might cause some problems. Dumbledore too would likely play a role. He might have some knowledge about the situation that he's not sharing right away, and his interactions with Severus would be crucial in determining Harry's fate.