One common plotline is Percy finding out that the Olympians have been using him all along. For example, they might have sent him on dangerous quests not just to save the world but also to gain more power for themselves. Another could be Percy being betrayed by a close friend or ally who is working for the Olympians' self - serving plans. Maybe they set him up to take the fall for something he didn't do.
Ares could be a likely character. He's always been somewhat of a wild card in the Percy Jackson series. He might betray Percy for his own amusement or to gain more influence in Olympus. Another could be Zeus. He's often paranoid about his power and might see Percy as a threat and betray him to protect his throne.
Well, in this 'percy is raised on olympus fanfiction', it might focus on Percy having to adapt to the unique environment of Olympus. He would be surrounded by powerful deities. It could show his training, his education in the ways of the gods, and his adventures within the realm of Olympus, all while being raised there.
Maybe he has some bad experiences with the Olympian gods in the original story, and in fanfiction, those negative feelings are amplified. For example, he might be tired of the gods' constant interference and manipulation.
It's not likely that the actual Olympus (in the context of the Percy Jackson series being a place of the gods) reads fanfiction. Fanfiction is a creation of the fans in our world, and there's no indication in the books that the gods or Olympus as an entity would engage with it.
Obviously, Percy would be one of the main characters. And probably the Olympian gods like Zeus, Poseidon, Athena etc. would also play important roles as he is raised in their domain.
Many 'Percy Saves Olympus' fanfictions also explore the theme of the clash between the modern world and the world of Greek mythology. Percy, being a modern - day demigod, has to navigate both worlds, and this creates interesting scenarios. For instance, he might use modern technology to defeat ancient monsters while saving Olympus.
Power struggle is a very common theme. It's about Percy and the demigods fighting against the all - powerful Olympians, showing a battle between different levels of power. Another common theme is loyalty. Percy has to decide where his loyalty lies, with his friends and fellow demigods or with the Olympians who have their own agendas.
In fanfiction, the politics and intrigues within Olympus might be depicted in a way that makes Percy disgusted. The backstabbing and power - hungry nature of some of the Olympians could be too much for him to bear, so he hates Olympus.
In this fanfiction, perhaps Percy is influenced by some dark force. This force convinces him that the Olympians are corrupt and need to be overthrown. He then betrays them by stealing important artifacts from Olympus that are crucial for its protection. He might also try to turn the demigods against the Olympians.