Perhaps there are other hackers in an underground hacking group that Percy gets involved with. These characters could have their own motives and personalities. Some might be in it for the money, while others for the thrill or to expose corruption. And there could be a love interest who either supports or is against Percy's hacking activities, adding a whole new dimension to the story.
I'm not sure specifically since I don't know the exact fanfiction, but it could be his friends who might be either involved in his hacking activities or completely unaware of them. Maybe there's a mentor - like figure who guides him in the world of hacking.
Well, there could be antagonists too. There might be rival hackers who are constantly trying to outdo Percy or stop him from achieving his goals. And then there could be characters from the 'normal' world, like his family members or colleagues at work/school who have no idea about his secret hacking life. Their reactions if they ever find out would be an interesting part of the story.
Well, without actually reading the fanfic, it's hard to say for sure. But it could be his friends. In many fanfics, there are often sidekicks or best friends who play important roles. They might support Percy in his adventures or add some comic relief to the story.
There could be new characters introduced as well. Maybe other gods or demigods who have a particular interest in Percy's new - found godhood. They could either be allies or antagonists, depending on their motives and how Percy's new power impacts the existing power balance in the fanfic's universe.
Grover could also be a main character. He might be at the scene when Percy gets drunk and try to use his nature - related powers to sober Percy up. Grover could also provide some comical relief with his reactions to Percy's drunken state, like his horrified expressions or his attempts to herd Percy like he would a wild animal.
Often in these types of fanfictions, aside from Percy, there might be minor characters that serve as catalysts for his actions. It could be a random villager who Percy saves, which then sets off a chain of events. Or perhaps an old mentor figure who appears briefly to give Percy some advice that helps him in his one - man battles.
Well, there could be a wise old wizard who discovers Percy. The wizard takes it upon himself to protect Percy from the forces that might be after him because of his mysterious origins. He becomes like a mentor to Percy, teaching him about the magical world and how to control his powers.
A young mermaid named Ariel could be a main character. She could be Percy's friend and help him explore the underwater world. She could teach him how to swim faster and find the best hiding places from the bigger sea creatures.
Nico di Angelo could be a central character. Given his connection to the underworld and his own complex relationship with the gods, he might be the one who has the most knowledge about what really happened to Percy and how to reverse it. He could be on a quest to bring Percy back from the dead, facing many challenges along the way.
There could be a new, made - up character. This character could be a seer who had foreseen Percy causing the earthquake but was unable to prevent it. Now, this seer has to work with Percy to understand why it happened and how to prevent future disasters. Or it could be a young demigod who looks up to Percy and is now caught in the middle of the chaos Percy has caused and has to learn to be brave and helpful during this crisis.
Annabeth could be one of the main characters. She might be torn between staying with the gods and following Percy. Their relationship could be a central part of the story as she tries to convince him to stay or decides to go with him.
There could be a strict drill sergeant as one of the main characters. This person would be constantly pushing Percy to his limits and teaching him discipline. Another character might be a fellow student who becomes Percy's best friend. They could support each other through the tough times at military school.