He'd be more cunning. In Gryffindor, Harry was brave and impulsive. In Slytherin, he'd learn to think before acting. He might also become more ambitious, not just about defeating Voldemort, but about changing the reputation of Slytherin.
Harry's character would experience a significant transformation. In Slytherin, he'd be surrounded by different values. His Gryffindor courage would still be there, but it would be tempered with Slytherin cunning. He'd have to deal with the Slytherin's reputation for Dark Arts, either by trying to distance himself from it or by reforming the perception from within. His self - identity would be in flux as he straddles the line between the heroic Gryffindor he was expected to be and the shrewd Slytherin he now is. He'd also face challenges in terms of loyalty, as Slytherin's loyalty is often more conditional compared to Gryffindor's.
At first, Harry might be confused and a bit out of place. He's used to the Gryffindor way of thinking. But in Slytherin, he has to adapt. He becomes more cunning in a positive sense. He learns to think on his feet and use his wits in different ways than he did in Gryffindor. For example, instead of charging into a situation like he might have in Gryffindor, he starts to plan more carefully.
His character would become more complex. He'd have to balance his own values with the Slytherin ideals. Harry would likely become more politically astute as he'd have to navigate the power plays within the Slytherin house.
When Harry is in Slytherin in fanfiction, his view of the wizarding world may change. He may start to see the grey areas more clearly. Instead of seeing things as simply good or bad, he realizes that there are many factors at play. This makes him more complex as a character. He may also have to deal with the Slytherin legacy of the Dark Arts. He has to navigate through the temptations and warnings related to it. He might study some Dark Arts spells not to use them for evil, but to understand how to defend against them, which is a very different path from what he would have taken in Gryffindor.
Hermione's character development could involve her learning to balance her traditional values with the new ones in Slytherin. She might start to value self - preservation more, as it is a trait often associated with Slytherin. This could make her a more well - rounded witch, not just relying on her Gryffindor - like courage all the time. Draco, on the other hand, could become more empathetic. Seeing Hermione face the challenges of being in Slytherin as an outsider could make him realize how wrong some of his previous actions were, and he could grow to be more inclusive.
One interesting fanfiction could be 'The Slytherin Prince Harry'. In this story, Harry's sorting into Slytherin changes his whole Hogwarts experience. He has to deal with the prejudice from the Gryffindors while also trying to find his place among the Slytherins. It shows a different side of Harry, more cunning and politically aware.
Well, he might face a lot of challenges. In Slytherin, he'd be surrounded by students with different values compared to Gryffindor. He could have a tough time making true friends at first. But it might also give him a chance to change the perception of Slytherin from within. He could use his Gryffindor courage to influence the more cunning and ambitious Slytherins towards a more positive path.
He'd likely be more inquisitive about different forms of magic. Instead of just relying on the spells taught at Hogwarts, he'd constantly seek out new magus - based knowledge.
Harry would likely become more feared by some in the wizarding world. Since the Basilisk is often seen as a terrifying and dangerous creature, his connection to it might make others view him with suspicion. He would also have to grapple with the darker side of magic that the Basilisk represents, which could make him more brooding and introspective.
Harry develops a different sense of loyalty. In a Slytherin environment, loyalty is often more conditional. So he learns to balance his own values with the more self - serving loyalty that exists in Slytherin. He may still hold onto his core beliefs of right and wrong, but he also understands the need to look out for himself and his housemates in a more Slytherin way. This could mean being more selective about who he trusts and how he shows his trust. He also becomes more aware of the power dynamics within the house and the wizarding world in general. He has to use his new - found Slytherin skills to survive and thrive, which changes his character in a more calculating and politically - aware way.
In these fanfics, Harry often becomes more calculating. For example, in some, he uses his Slytherin cunning to outwit his enemies instead of just relying on his Gryffindor courage. He learns to look at situations from multiple angles.