Well, there's often the theme of understanding. Percy, with his rather rigid view of the world, can learn to understand Harry's more unorthodox ways. And Harry can understand Percy's need for order and achievement. Another theme is loyalty. They can show loyalty to each other in the face of various challenges in the wizarding world, be it from dark wizards or from the corrupt parts of the Ministry of Magic.
One common theme is redemption. Percy has his moments of being on the wrong side in the original series, so in fanfiction, his relationship with Harry often serves as a way for him to redeem himself. For example, Harry might be the one to help Percy see the error of his ways.
A common theme is the growth and change of the characters. For Percy, his relationship with fem Harry can make him more open - minded and less rigid. For fem Harry, it can be about finding a different kind of support system outside of her usual friends. Also, the theme of family acceptance is often there. How will the Weasley family accept fem Harry as Percy's potential partner? And how will Harry's own friends react?
There are. A lot of fanfictions play with the idea of Percy mentoring Harry in some way. Percy has a lot of knowledge about the wizarding world's rules and regulations, and he could help Harry navigate through some of the more bureaucratic aspects, like dealing with the Ministry's paperwork when it comes to things like Quidditch regulations or magical creature rights.
One common theme is redemption. Percy has made mistakes in the original series, and many fanfictions focus on him making up for those, often with Harry's help. Another theme is friendship. They are from different generations in the Weasley family, but fanfictions explore how they can form a strong bond.
One common theme is friendship turning into something deeper. Another could be the exploration of their different personalities and how they complement each other.
Often, there's a theme of missed opportunities. Harry is so busy with his own problems that he misses out on a relationship with Ginny. There might also be a theme of friendship being tested. Since Ginny is part of Harry's friend group, his ignoring her can cause tension among the friends.
Friendship is also a big theme. Their relationship is often portrayed as a deep and meaningful friendship that can withstand any difficulties. They support each other through tough times, like when Harry has to deal with Voldemort and Charlie is there to offer his expertise on magical creatures.
One common theme is the exploration of forbidden love. Since they are from different generations in the wizarding world, there's an element of this relationship being something that others might not easily accept.
One common theme is family. Given Percy's complex family situation in the Harry Potter series, fanfictions often explore how Audrey fits into the Weasley family. Another theme is love and acceptance. Writers may show how Percy, who was once a bit of an outcast in his family, finds love and acceptance with Audrey.
One common theme is isolation. In these fanfictions, Percy often feels alone, cut off from his family and former friends due to his actions or decisions. For example, in many of them, his decision to side with the Ministry during certain events causes a rift that makes him feel like an outcast.