A possible fanfiction plot could be that Draco, now a girl, discovers new magical abilities that were suppressed in his male form. These powers could be related to a more intuitive connection with magic, something that is often associated with femininity in the wizarding world. This newfound power could put her in a position where she has to choose between using it for the benefit of Slytherin or for the greater good of Hogwarts, creating a moral dilemma for her character.
His personality might become more empathetic. As a girl, Draco could start to see things from a different perspective. For example, he might be more sensitive to the way others are treated, especially other girls in Hogwarts.
In terms of his relationships with his Slytherin peers, some might look down on him. But others could be intrigued. Pansy Parkinson, for example, might see Draco as a girl as a threat to her status as the 'queen bee' in Slytherin. However, some of the more open - minded Slytherins could befriend Draco and help her deal with the challenges of being a girl in a very traditional and often misogynistic wizarding society.
In the Hogwarts hierarchy, things would change. Hermione is often seen as a bit of an outcast by some Slytherins because she's a Gryffindor. Draco, now in her body, would face a different kind of discrimination or at least a lot of strange looks from his own housemates. He would also have to deal with Hermione's reputation among the teachers. Some teachers might expect the same level of knowledge and participation from 'Hermione' (who is actually Draco), and he would struggle to meet those expectations.
In a fanfiction, Draco could be chosen as an unwilling participant in the Triwizard Tournament. Maybe the Goblet of Fire was tampered with by some dark forces who thought Draco would be an easy puppet. As he goes through the tasks, he starts to show unexpected courage and loyalty, much to everyone's surprise.
Well, a plot could involve Draco as a girl being in a love triangle. Maybe she has feelings for Harry, but at the same time, there's a Slytherin boy who has been in love with her for years. This could lead to a lot of drama and conflict within the Slytherin house and also between houses. Also, her family might react differently to her as a girl, perhaps her father has different plans for her than he would for a son, and she has to deal with that.
Another way could be through a potion gone wrong. In the wizarding world, potions can have all sorts of strange effects. If Draco was trying to brew a potion for some other purpose, like trying to gain an advantage in a competition or something, and made a mistake in the ingredients or the brewing process, it could result in him being transformed into Hermione. This would force him to experience life from her perspective, which could be a huge character - development opportunity for him.
In a fanfiction where Draco Malfoy and a Muggle have a baby, there could be a lot of conflict. The wizarding world might not accept the baby easily due to its Muggle heritage. Draco could struggle with protecting his family from the prejudice of his own kind. He might have to make difficult choices between his loyalty to the wizarding world and his love for his Muggle - born family.
A possible plot in such a fanfiction could involve Draco seeking help from unlikely sources. Maybe he goes to Hermione Granger for advice, since she's known for her intelligence and knowledge. This could lead to an interesting dynamic between the two former rivals. The story could also explore how Draco deals with the practicalities of pregnancy, such as dealing with morning sickness while still trying to maintain his status in the wizarding community.
One idea could be a story where Scorpius discovers a long - hidden family secret that Draco has been trying to protect him from. It could involve some dark magic from their family's past.
A really interesting plot could be that Draco's transformation into a girl is part of a bigger magical mystery. She starts to notice strange things happening around Hogwarts that seem related to her change. As she tries to figure out what's going on, she teams up with unlikely allies from different houses. Along the way, she also has to deal with the prejudice and confusion from some of the wizarding community who don't understand or accept her new identity.