Well, in some fanfics, Slytherins might be protective of Harry in an abuse scenario because they see the injustice. They could be written as having a sense of fairness that overrides the typical house rivalries. Maybe they've come to understand Harry's situation better than others and feel compelled to protect him.
In abuse - related fanfics, Slytherins being protective of Harry can be a way to explore different character dynamics. It breaks the mold of the typical Hogwarts houses' relationships. Slytherins might be written as having a hidden soft side that emerges when they see Harry being abused. It could also be that the author wants to create a more inclusive and diverse story where traditional enemies can become allies.
The themes often involve loyalty. Slytherins in these fanfics show loyalty to Harry in a way that goes against the stereotype of their house. Some fanfics also have the theme of family. Maybe a Slytherin character sees Harry as a surrogate family member and will do anything to protect him. There are also themes related to justice, where Slytherins protect Harry because they know he's the key to a just future for the wizarding world.
In some fanfics, Slytherins might learn of Harry's abuse through rumors that spread within Hogwarts. For example, students could overhear conversations among the Gryffindors who know about Harry's difficult past with the Dursleys. Another way could be if there are certain events that expose Harry's past abuse, like a confrontation where Harry's secrets are accidentally revealed in front of Slytherins.
There are quite a few. Some fanfics focus on individual Slytherin students who form an unlikely bond with Harry. They might protect him from the dark forces that are after him, seeing him as more than just the 'Chosen One' but as a friend in need. These fanfics often explore the idea that not all Slytherins are bad and can be quite heroic when it comes to protecting someone they believe in.
There's also 'The Slytherin Guard for Hermione'. This fanfic shows how some Slytherins, who have grown tired of the house's bad reputation, choose Hermione as the symbol of their change. They protect her from dark wizards who target her for her Muggle - born status. It's an interesting take on how Slytherins can be allies.
There could also be a change in the overall dynamic within Hogwarts. If Slytherins learn about Harry's abuse, it might cause a shift in the traditional rivalries between Gryffindor and Slytherin. Some Slytherins might start to question the way they have always treated Harry and the other Gryffindors, leading to a more complex and nuanced relationship between the two houses in the fanfic world.
One reason could be that they see her intelligence as an asset. Hermione is known for her brilliant mind, and Slytherins, who value cunning and resourcefulness, might respect that. They could also recognize her strength in the face of adversity and be drawn to protect her as a way to show their own growth beyond the typical Slytherin - Gryffindor rivalry. In some fanfictions, a Slytherin might have a personal connection or debt to Hermione, which leads to their protective nature towards her.