Obviously, Percy Jackson himself. Since it's about him being the son of Amphitrite. Also, Amphitrite is likely to be a main character, as she is his mother. Other characters could include his friends from Camp Half - Blood, like Annabeth, who might have to deal with Percy's new identity and the changes it brings.
Percy is the central figure, of course. But we may also see Triton, Amphitrite's son in the original mythology. He could be a complex character in the fanfiction, perhaps having a conflicted relationship with Percy. And then there are the sea nymphs and other minor sea deities that might be involved, either as allies or antagonists depending on the story.
The main characters would definitely include Percy. Then, there could be characters from the underwater court. For example, the mermaids and mermen who serve Amphitrite. They could play important roles in helping Percy understand his new heritage and powers. And let's not forget Poseidon. Even though Percy is now seen as the son of Amphitrite, Poseidon's influence might still be present, and their relationship could be explored in the fanfiction.
Percy is, of course, the main focus. However, in many of these fanfictions, Luke Castellan can also be a major character. Since Luke had his own issues with the gods and turned to the dark side in the original series, he could either be an influence on Percy's dark turn or an ally in his new dark journey. Nico di Angelo is another character who could be involved. Given his connection to the Underworld and his own complex relationship with Percy, he might try to understand what's going on with Percy or try to fight against him if he thinks Percy has gone too far.
Percy Jackson himself is obviously a main character. His struggle with bloodlust is often the central focus. Annabeth Chase also frequently appears as she tries to help Percy deal with his issues, using her intelligence and strategic thinking.
Obviously, Percy Jackson himself is often a main character. His ability to control water can be crucial when dealing with the effects of the Earthshaker, like tsunamis caused by the earthquakes. Annabeth Chase is also likely to be involved. Her strategic mind can help in planning how to approach the situation with the Earthshaker.
Percy Jackson himself is often involved. He might encounter the wolf in the woods around Camp Half - Blood and have to figure out if it's a friend or foe. Another common character is Annabeth. She could use her wisdom to analyze the significance of the wolf in the context of the Percy Jackson lore.
Percy Jackson himself is often the main character. He has a connection to the sea, and in pet fanfiction, he might find a sea - related pet like a hippocampus that he befriends and trains. Annabeth Chase could also be involved. She's smart and might use her knowledge to help with any problems the pet causes or gets into.
Obviously, Percy Jackson himself is often the central character in such fanfictions. His friends like Annabeth Chase can also be involved. In some cases, she might be the one trying to keep Percy out of trouble or, on the contrary, joining him in his 'delinquent' adventures. Grover could also be there, perhaps reluctantly getting dragged into Percy's misadventures.
In these types of fanfictions, Nico di Angelo could play a significant role. Given his connection to the underworld, he might be involved in trying to either retrieve Percy's soul or deal with the after - effects of his death. Also, Luke Castellan's spirit could make an appearance, maybe taunting Percy in his final moments or having some role in the events leading up to his death.
Some of the traditional sea monsters like the Kraken could be antagonists. Since Percy is now in a more prominent position in the sea world as Amphitrite's adopted son, the Kraken might see him as a threat and try to attack him.
Percy Jackson himself is often a central character. Given his connection to the sea and his heroic status in the original series, he's likely to be involved in any story related to the primordial thrones. He might be on a quest to understand or protect the thrones.
Percy Jackson himself is often involved. Since he's the main character in the original series, it makes sense that he'd be at the center of these genetic experiments in fanfiction. Maybe he's the subject of the experiments, or he's the one trying to stop some unethical genetic experiments from happening.