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.
One idea could be that Harry and the Weasley twins team up to play a huge prank on Snape. They use a combination of Fred and George's magical inventions and Harry's invisibility cloak to get into Snape's office and rearrange everything in a really chaotic way.
One idea could be the twins inventing a new type of magical prank product that has unexpected effects on Hogwarts. For example, it might make the staircases act even more erratically than normal, causing chaos throughout the school.
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.
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.
One idea could be that they discover their twin bond gives them unique powers. For example, they can combine their skills in combat, like Percy's water control and Thalia's lightning, to defeat a powerful enemy. Another plot could involve them exploring their family history together, finding out secrets about their parents that change their view of themselves. Maybe they meet a relative who knew about their twin relationship all along but was sworn to secrecy.
One plot idea could be that Percy and Jason discover they are twins in a very unexpected way. Maybe during a quest, they start having the same strange dreams and realize they have a deeper connection. Another could be that they have to team up against a powerful enemy who is specifically targeting them because of their unique twin bond.
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.
Another plot could be that the OC is a muggle - born with an uncanny ability to see through magical illusions. The Weasley twins, known for their love of creating illusions, initially see the OC as a threat to their pranks. But as they get to know the OC better, they realize that they can use this ability to create even more elaborate and undetected pranks. This would involve a lot of character development for all of them as they learn to trust and rely on each other.
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.