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.
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.
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.
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.
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.
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.
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.
Artemis could be a major character. As the goddess associated with the Hunt, she would have a huge role. She might initially be skeptical of Percy's ability to protect the Hunt but gradually come to trust him. Thalia, who is part of the Hunt, would also be important. She has her own history with Percy and could be a key ally in the protection efforts.
Definitely the dragons would be key characters. There could be a powerful dragon queen who takes Percy under her wing, so to speak. She would be a very important figure in Percy's upbringing, teaching him the values and ways of the dragons. And there might be an outcast dragon, shunned by the others, but who bonds with Percy because they both feel like outsiders. Also, some of Percy's original friends from the demigod world, like Annabeth, might make an appearance. She could be initially confused and then intrigued by Percy's new dragon - influenced self.
Annabeth could be a main character. She might be desperately trying to find Percy after he jumps off Olympus. She could use her wisdom and strategic skills to track him down, facing various obstacles along the way, like mythical beasts or other unfriendly demigods. Another character could be Grover. He could sense Percy's distress and join Annabeth in the search, using his nature - related powers to help them.
There might be a monstrous creature that Percy befriends instead of fighting. This creature could have unique abilities that help Percy survive, like being able to sense danger from afar.