Maybe because some fans want to explore a different side of Harry. By making him the 'king' of Slytherin, they can show how his character could adapt and thrive in a different house's environment.
In fanfiction, creativity knows no bounds. Fans might make Harry the king of Slytherin to subvert the traditional narrative. They could be interested in showing how Harry, with his own set of qualities like bravery and loyalty, could influence and change the Slytherin house for the better. Or perhaps it's a way to explore a more complex and morally grey Harry Potter, who can navigate the often - misunderstood Slytherin culture and bring out the best in it.
For entertainment. Just like anyone else, Slytherin students would be interested in exploring different stories set in the Harry Potter universe.
Obviously, Harry Potter himself is crucial. Then there would be the other Slytherin students like Draco Malfoy. Their relationship could be very different in this fanfiction. Maybe they become allies instead of rivals. There could also be the Slytherin professors who play important roles in guiding Harry as the new 'king' of the house.
It could mean that in certain fan - created stories (fanfiction), Harry Potter is depicted as a dominant or important figure within Slytherin. Maybe in these fictions, he has extraordinary power or influence within the Slytherin house, which is quite different from his traditional Gryffindor identity in the original series.
Perhaps it's a symbol of unity. The fanfiction author might be exploring the idea of breaking down the house rivalries, and Harry wearing the Slytherin tie is a physical manifestation of that. He could be trying to show that Hogwarts should be united regardless of house.
Obviously, Harry Potter himself as the Ice King. Then there would be Draco Malfoy. He could be either a rival or an ally to Harry in this new role. Hermione would also be there, trying to understand the magic behind Harry's transformation and helping him control his powers. And of course, Snape, who might have some knowledge about the Slytherin magic related to the Ice King.
Well, a great plotline might be Harry delving into the history of Slytherin. He could discover secrets about the founder that give him an edge in leading the house. For example, he might find hidden chambers or spells that only the true heir of Slytherin should know. This could lead to him using this knowledge to protect Slytherin students from discrimination and also to gain respect within the wizarding world as a Slytherin leader.
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.
One great Slytherin - centered fanfiction is 'The Slytherin Heir'. It delves into the life of a Slytherin student who discovers a hidden secret about their family's connection to the Slytherin legacy. The story is filled with complex characters and a plot that keeps you guessing.
Maybe it's a new Slytherin character created specifically for the fanfiction. This character could be someone who has always admired Harry from afar and decides to take a chance on courting him. They might have different qualities from the typical Slytherins we know in the original books, being more open - minded and brave in their pursuit of Harry.
They're interesting because they break the mold. In the original series, Harry is firmly in Gryffindor. So, when he's a Slytherin in fanfictions, it completely changes the dynamics. For example, his relationships with characters like Hermione and Ron would be very different. He might not be as close to them, and instead, form new friendships within Slytherin.