His relationships change drastically. For example, Hermione might be initially very suspicious of him being in Slytherin. Ron might be more openly hostile at first. But as the story progresses, Harry could prove that just because he's in Slytherin doesn't mean he's a bad person. His relationship with Snape could also be different. Snape might still dislike him, but for different reasons related to Slytherin house politics.
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.
Well, he might face a lot of internal conflict. In the original story, Slytherin is seen as the house of the 'bad guys' to some extent. So Harry would have to deal with the prejudices of his Gryffindor - loving friends. He could also find some unexpected allies among the Slytherins who might see his potential and his fame as something useful. Maybe he would start to understand the Slytherin values in a different way, like ambition not always being a bad thing.
He might start by promoting fairness and equality within Slytherin. In the original series, Slytherin is often associated with pure - blood supremacy. Harry, as head, could break that stereotype. He could encourage students from all backgrounds to work together and support one another, changing the cut - throat competition within the house to a more collaborative environment.
Well, usually it changes the relationships. For example, his friendship with Ron and Hermione might be strained at first. Since they are in different houses. Harry might also face different types of rivalries within Slytherin. He has to prove himself to his new housemates.
An intelligent Slytherin can have a huge impact on the plot of Harry Potter fanfiction. Slytherins are typically portrayed as shrewd and resourceful. So, in fanfic, an intelligent one might be able to outwit Voldemort or his Death Eaters in ways Harry and his friends couldn't. They could use their intelligence to broker peace between the houses at Hogwarts, which would be a major shift from the often - tense relationships in the original series. They might also introduce new magical concepts or techniques that they've discovered through their own research and study, opening up entirely new storylines and directions for the fanfiction.
It makes him more cynical. Harry, after experiencing abuse, is less trusting when sorted into Slytherin. He uses the house's cunning to protect himself from further harm.
Harry's character would experience a significant shift. In Slytherin, he'd be surrounded by students who are often more politically astute. This would cause him to grow in that regard. He might learn to use his words more carefully and be more strategic in his relationships. His moral compass would still be there, but it might be tested more frequently as he tries to fit into a house known for its more self - serving tendencies. He could end up becoming a bridge between the two houses, Gryffindor and Slytherin, with a character that combines the best of both worlds.
The story would change a great deal. In the original, Harry being in Gryffindor meant he was associated with courage and heroism. In Slytherin in fanfiction, he'd be associated with cunning and ambition. The Sorting Hat's decision to put him in Slytherin would likely be due to some different interpretation of his character traits. Maybe it saw his ambition to defeat Voldemort as more of a Slytherin - like quality. This would also change how the teachers view him. Snape, for example, might be less hostile towards him since they are in the same house.
His character becomes more calculating. In Slytherin, he has to adapt to the house's values of cunning. So, he might think twice before acting, unlike his more impulsive Gryffindor self. For example, in a duel, he would strategize more instead of relying solely on courage.
His story would change a great deal. He might not be as much of the center of attention as he was in Gryffindor. In Hufflepuff, he'd have to work harder to stand out in a different way. Instead of being known for his bravery in the face of danger all the time, he could be recognized for his loyalty and fair play. His enemies might also underestimate him more since Hufflepuff doesn't have the same 'daring' reputation as Gryffindor.