One idea could be Percy being sorted into Slytherin instead of Gryffindor and how that changes his relationships with his family. For example, he might have a more strained relationship with his Gryffindor siblings at first. Another plot could be Percy using his Slytherin cunning to outwit his political rivals in the Ministry of Magic later in life. Or perhaps a plot where Percy has to team up with some Slytherin students to solve a mystery that the Gryffindors are too head - strong to figure out.
A really interesting plot could be Percy's struggle to fit in Slytherin while still holding onto some of his Gryffindor values. He could be constantly torn between the two houses' ideals. There could also be a plot where Percy discovers a secret society within Slytherin that has some dark intentions, and he has to decide whether to expose them or join them. And what about a love story? Maybe Percy falls in love with a Slytherin girl, and they have to overcome the prejudices of their respective houses.
In some Slytherin Percy Weasley fanfictions, there might be a plot where Percy uses his Slytherin - like ambition to climb the ranks in the wizarding world much faster than he did in the original story. He could be making some morally grey decisions along the way. Another idea is that Percy, as a Slytherin, has a different view on the war against Voldemort. He might be more inclined to find a diplomatic solution rather than a full - on battle approach. This could lead to a lot of conflict with his family and friends who are more on the side of direct confrontation.
One idea could be Percy trying to understand the twins' pranks and finally joining in on one. Another could be the twins getting Percy to loosen up during a stressful time at Hogwarts, like exam week. Maybe they play a prank that backfires and Percy has to help them fix it without getting in trouble with the professors.
Another plot could involve Percy being assigned to work with Hermione on a top - secret project at Hogwarts. Maybe it has something to do with protecting ancient magic texts. Along the way, they learn to respect each other's different approaches and form an unlikely friendship.
Maybe a fanfiction where Percy and his family get magically transported to a different era. They have to rely on each other and their family bonds to find a way back. Percy, being the rule - follower, might struggle at first with the lack of established rules in this new situation, but then he realizes the importance of his family's more flexible ways.
Well, a plot could be that Ginny is a Slytherin spy within Gryffindor. She's secretly feeding information to Slytherin about Gryffindor's plans in Quidditch or other competitions. But as she does this, she starts to feel conflicted because she really likes her Gryffindor friends.
The contrast. Percy is known for his Gryffindor traits like loyalty (to a fault) and bravery in his own way. But in Slytherin, he has to adapt to a different set of values. His ambition might take on a new form, and seeing how he balances his old self with the Slytherin side is really engaging.
A third plot could revolve around Percy's family relationships. He could be feeling overshadowed by his more popular siblings. So, he decides to prove himself in a different way. He enters a magical competition that tests not only magical skills but also strategic thinking. Along the way, he learns to appreciate his family more and they start to see him in a new light.
A plot could revolve around Percy being sent on a mission by the Order of the Phoenix that is similar to what the Scarlet Pimpernel did. He has to assume a false identity in the Muggle world while also dealing with his own insecurities and the expectations of his family back in the wizarding world. Along the way, he meets a Muggle girl who he falls in love with, but he has to keep his true identity a secret from her, adding a romantic sub - plot to the fanfiction.
One interesting plot idea could be the initial shock and resistance from both Hermione and Percy. Hermione, being a strong - willed and independent witch, might fight against the marriage law at first. Percy, on the other hand, is very rule - abiding, so he might initially try to force the marriage to work just because it's the law. They could start off clashing over their different views on the situation. For example, Hermione might be more focused on finding a way to repeal the law while Percy is more concerned with following the regulations. As they spend more time together, they could gradually discover each other's hidden depths and start to develop real feelings for one another. Maybe Hermione realizes that Percy has a more creative side beneath his uptight exterior, and Percy discovers Hermione's vulnerability.
Perhaps there could be a time - travel plot where Hermione and Percy are sent back in time together. They have to rely on each other to get back to their own time. During this adventure, they see different sides of each other. Percy sees Hermione's quick thinking in a completely different context, and Hermione sees Percy's loyalty to his family and friends in a new light, which could lead to a romantic relationship.
Maybe in the fanfiction, there's a situation in a collapsing wizarding building. Fred is trapped under some rubble and Percy, using his skills and knowledge of magical architecture, manages to find a way to free Fred. As they escape, they start to realize how much they've missed having a proper relationship with each other, and Percy makes a vow to always be there for Fred.