It's likely that Chiron, the centaur, is also a main character. He has a wealth of knowledge and experience and can guide Percy and the other demigods in using their powers effectively to protect the camp. He might also be involved in training them and preparing for different types of threats that Percy's powers need to counter.
Well, perhaps Percy uses his water - controlling powers to fend off a horde of mythical monsters attacking the camp. He could create huge waves to sweep them away.
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.
In this fanfiction, Percy is the main one in control. But characters like Chiron, the centaur mentor, would also play a significant role. Chiron has a wealth of knowledge and experience, and Percy would likely rely on him for advice on matters of the camp's history and traditions. Also, there could be some antagonist characters within the camp who don't like Percy's new rules and ways of controlling, which would add some conflict and drama to the story.
Some of the Roman gods or goddesses might also play important roles as characters. They could interact with Percy in different ways compared to how they interact with the Roman demigods in the camp. For instance, if Jupiter shows up, he might have different expectations of Percy compared to Poseidon, Percy's father in Greek mythology.
Obviously, Percy Jackson himself would be a main character. Since it's about him being in a god camp. Annabeth Chase is also likely to be a main character as she has always been an important part of Percy's life. Grover, Percy's best friend, would probably be there too. And there might be some new characters, like other god - like beings or powerful demigods in the camp that Percy interacts with.
Percy is the obvious main character. There could be his friends from previous adventures who accompany him to the camp. Additionally, there might be a villain in the story who is misusing the fish blood. This villain would be an important character as they would drive the conflict in the fanfiction. There could also be some local creatures at the camp that are affected by the fish blood and they could be important characters as well.
It could be a rogue demigod who is jealous of Percy's powers and wants to stop him from mastering them. This demigod might have some dark powers of their own and would constantly set up traps and challenges for Percy. For example, they could use illusions to make Percy doubt his own powers and abilities.
Obviously, Jason and Tim are the main characters. Jason is the protector and Tim is the one being protected.
Maybe there are some dark forces at work. They sense Percy's growing power and want to stop him before he becomes too strong. These could be ancient evils that have been awakened by Percy's power development. They could send minions or create illusions to make Percy's training difficult.
It's hard to say for sure. Maybe his friends are characters that are common in the genre it belongs to. They could be fellow students if it's a school - based setting, or comrades in an adventure - filled world. They might have different personalities and abilities that complement Percy's in some way, like one being good at healing and another at finding hidden paths.