Well, in addition to Percy, there could be a character like Chiron. Chiron could play a crucial role in guiding Percy, teaching him how to control his powers and deal with the prejudice. Also, a powerful goddess, say Athena, could be involved. Since Arachne had a history with Athena, Athena might be interested in Percy, either to test him or to use him for her own purposes. And of course, Percy's father figure (whoever that may be in this fanfic's universe) could be an important character as well, providing moral support and training.
Annabeth could be a main character. She might be initially distrustful of Percy because of his mother but then come to see his true worth. Another could be Grover, Percy's loyal friend, who stands by him through all the difficulties. There could also be new characters, like a half - spider half - human hybrid who is Percy's distant relative and helps him understand his heritage.
Besides Percy, there could be a group of outcast demigods. These are demigods who, like Percy, have a 'tainted' parentage or are otherwise not fully accepted in the demigod community. They form a sort of misfit gang with Percy, and together they fight against the discrimination they face. There could also be an antagonist, perhaps a demigod who is jealous of Percy's unique powers and tries to undermine him at every turn.
One possible plot could be Percy, as the son of Arachne, struggling to fit in among the other demigods. He might have unique powers related to weaving and spiders, like being able to create illusions with spiderwebs. He could be initially feared or shunned because of his mother's reputation, but then prove himself a hero by using his powers in creative ways to defeat monsters.
There could be his friends or comrades in the hunt. For instance, someone like Annabeth who might be affected by his leaving and try to convince him to stay.
There could be an alien sidekick named Zorx. Zorx might be a small, furry creature with the ability to see in multiple spectrums, which helps Percy navigate through different planetary environments.
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.
Annabeth could be a main character. She might be skeptical at first about Percy's new ability to control Styx, but then she uses her wisdom to help him understand the implications and possible uses of it. For example, she could research ancient texts to find out if there are any hidden dangers or benefits to Percy's control.
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.
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.