One possibility is that there is a great celebration among the gods and they invite Percy as a hero. They might bestow new powers or honors upon him. Or, on the contrary, there could be some gods who are jealous of Percy's popularity among mortals and demigods and try to undermine him during the meeting.
I think Poseidon is a must - he's Percy's father, after all. Then there's Zeus, who likes to be in control and would want to see this baby who could grow to be a significant force. Apollo might come just for the fun of it, being the god of many things including prophecy, he might have some insights. And Artemis, as the goddess of the hunt, could also be there to see what all the fuss is about regarding baby Percy.
Well, it could be that the gods, being curious about this special baby Percy, come to visit him. Maybe they bring gifts like in the story of baby Hercules. They might see his potential and start to argue among themselves about his future role in the world of demigods.
Obviously, Percy is one of the main characters. And then there would be various gods like Zeus, Poseidon, Athena, etc. These gods play important roles in Percy's world and their interactions with him would be central to the story.
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.
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.
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.
One aspect could be that in many Percy Jackson - related fanfictions, Percy being betrayed by the gods often leads to a complete shift in his character arc. He might become more cynical or distrustful. For example, he could start to question his previous heroic deeds and wonder if he was just a pawn in the gods' games all along.
Yes, in some fanfictions, Percy is often reimagined as the king of the gods. Writers like to play with the traditional mythology and give Percy this exalted status for creative and interesting storylines.