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.
His character becomes more self - reliant. In these fanfictions, the abuse has toughened him up. Being in Slytherin, he has to rely on his own wits and the support of his new house, which is not always forthcoming like in Gryffindor. He learns to be more independent and not rely on others' heroics. For example, he might study magic more on his own to prove himself worthy in Slytherin.
Well, in Slytherin, Harry could end up being one of Snape's top students. This might lead to a more positive relationship. Snape might see Harry as a chance to redeem the Slytherin image. He could start to trust Harry more and share some of his knowledge about dark magic in a more open way, which was not possible when Harry was in Gryffindor.
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.
There's a fanfic titled 'Harry in Slytherin: Overcoming Abuse'. In it, Harry's sorting into Slytherin is a shock to many. But within Slytherin, he finds a sense of belonging. The house's values of ambition and self - preservation help him deal with his abuse. The story shows how he transforms his pain into strength with the support of his Slytherin peers. It's a story of redemption and growth.
One great fanfiction in this vein is 'The Slytherin Heir' where Harry, having endured abuse, is sorted into Slytherin. It delves into his complex relationships with his housemates and how he overcomes the stigma associated with Slytherin. The story shows his growth and development as he uses his Slytherin cunning to face the challenges in the wizarding world.
It makes Harry more complex. He has to deal with the darker side of his new identity. He might become more reserved as he tries to figure out what it means to be the heir of Slytherin.
Harry may become more cunning as he is in Slytherin. He might be more guarded in his actions and words.
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.
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 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.