Percy could add new realms for the gods to rule over. Such as a realm made entirely of music, where the god of music has absolute control. This would bring in new elements of culture and art into the fanfiction world of the gods.
He might introduce new relationships among the gods. Maybe a forbidden love between a god of the sun and a goddess of the night, which would create a lot of drama and conflict. This could lead to power struggles and changes in the divine hierarchy. He could also create new backstories for the gods, like a god who was once a mortal and achieved divinity through an extraordinary act of kindness.
By giving them unique physical features. For instance, a god with wings made of starlight.
Percy himself is obviously a must - include. His powers and his connection to Poseidon make him a central figure. Annabeth is also very popular. Her intelligence and her relationship with Percy add a lot of depth to the story. Grover is another great character. His loyalty and his role as a satyr can bring in some interesting elements, like his ability to sense danger and his connection to nature.
A new demigod who has a very different set of powers from Percy. This demigod could be from a previously unheard - of parentage among the gods. For example, a child of Hypnos, the god of sleep, who can put people into different levels of sleep - like a deep coma - like sleep or a trance - like state. This would add a new dynamic as Percy has to figure out how to work with someone with such a different power set.
Percy Jackson is likely still one of the main characters. After all, he's the central figure in the original series. And Annabeth might also be there, as she's always been by Percy's side.
Probably Poseidon, as he is Percy's father and has a vested interest in his son's well - being. Zeus might also be protective in some cases, despite their past differences, as Percy is a hero who often saves the world which benefits Zeus's realm as well.
Well, without reading the specific fanfiction, it's hard to say exactly who Percy is. But generally, in a 'champion of the gods' scenario, Percy would be a central figure. He might be a hero with unique powers, like being able to control certain elements or having superhuman strength. He could be a character who has to face various challenges and tasks on behalf of the gods, kind of like a chosen one in a fantasy story.
Well, one interesting concept could be the new power dynamics. With new gods introduced, it might change how Percy and his friends interact with the divine world. Maybe the new gods have different rules and values compared to the old ones.
Perhaps a fanfiction where the New Gods create a sort of competition for demigods. Percy enters this competition and discovers that there are rules he's not used to, and he has to use his wits and skills in new ways to win. And along the way, he makes some unexpected allies among the new gods.
The gods might show their protection in various ways. For example, they could directly intervene in battles Percy is in, using their divine powers to shield him from harm. They might also send him signs or omens to guide him away from danger.
Zeus is a possibility. As the king of the gods, he might see Percy's potential and adopt him to have an ally among the demigods. Another could be Poseidon, since Percy is already his son in the original story. It would be an interesting twist to have Poseidon formally adopt Percy in a more divine way.