Interesting fanfics often play with the idea of Percy using his intelligence, which was shown in the books, in the context of the Scarlet Pimpernel's adventures. Maybe he uses his knowledge of wizarding bureaucracy to outwit his enemies. Also, the relationships he forms during his Scarlet Pimpernel - like escapades, whether it's with old friends from Hogwarts or new allies, add depth to the story. The settings, too. If the fanfic takes Percy to different magical or Muggle locations, it can create a whole new world of adventure.
In the Harry Potter books, Percy was often seen as a bit of a stickler for propriety and status. In the role of the Scarlet Pimpernel, this could translate into him being very careful about his public image while secretly being a hero. He might use his knowledge of wizarding society's expectations to his advantage when it comes to hiding his true identity as the rescuer. Also, his pride could fuel his determination to be the best at his new role, just as he was proud of his achievements at school and in the Ministry.
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.
You could start by looking on popular fanfic websites like Archive of Our Own (AO3). Just search for 'Percy Weasley Scarlet Pimpernel' in the search bar and browse through the results. There might be some great stories there.
The Scarlet Pimpernel is Sir Percy Blakeney. He uses his charm and wit, along with his extensive network of contacts, to carry out his heroic deeds. His identity as the Scarlet Pimpernel is a well - guarded secret, and his wife, Marguerite, initially doesn't know about his alter ego. He's a symbol of courage and selflessness in the face of great danger during that tumultuous time in French history.
The Scarlet Pimpernel is very brave. He risks his life to save the French aristocrats from the horrors of the guillotine. He is also extremely clever. His disguises and strategies to outwit the French revolutionaries are very smart.