In a 'Percy Jackson leaves earth' fanfic, Percy could meet ancient celestial beings that predate the Greek gods. These beings could have knowledge and powers that Percy has never seen before. He might also run into some sort of interdimensional travelers who are exploring the universe just like he is, but with different motives.
He might meet other inter - galactic beings. For example, some sort of space - faring demigods from a far - off galaxy. Or he could encounter powerful entities that are the rulers of other planets.
Percy might meet an old enemy who has somehow been resurrected or changed in the future. This enemy could be more powerful and have a new plan to take over the world or destroy the demigods. Or he could meet a group of time - traveling demigods from an even further future who are trying to fix something in Percy's future that has gone wrong.
Percy might run into Loki. Loki is known for his trickery. He could either befriend Percy for his own devious plans or try to deceive him. Percy, being used to dealing with tricky situations in his own world, would have to be on his guard against Loki's schemes.
He might meet other demigods who are not affiliated with the camp. These could be demigods who have been living on their own, trying to hide from the monsters and the chaos of the demigod world. They could have different views on how to use their powers and might teach Percy new ways to fight or survive.
In a 'Percy Jackson leaves earth' fanfic, he might end up in a whole new realm of gods and monsters. Maybe he discovers a parallel universe where the rules of the Greek gods are different. He could encounter new versions of his friends or enemies and have to learn new powers to survive.
There might be some magical creatures in the school that Percy gets to interact with. Maybe centaurs who are teachers at the school or satyrs that are his classmates. These interactions would be really interesting as they could introduce Percy to new ways of thinking and different cultures within the world of the fanfic.
He might meet some native Alaskan spirits. These spirits could be like the nature spirits he has encountered before but with their own unique Alaskan characteristics.
He could meet some Aboriginal heroes or spirits. They might have their own powers and knowledge that Percy can learn from.
Percy might encounter Baba Yaga. She is a well - known figure in Russian folklore. She could be an adversary, testing Percy's skills and his knowledge of the magical world. Or perhaps she could be a source of information if Percy manages to earn her respect. He could also meet the Rusalki, water nymphs from Russian mythology. Given Percy's connection to water, it would be interesting to see how he interacts with them.
He could meet other demigods from different regions. For example, a demigod from Scandinavia with powers related to ice.
There's a chance that it could be a character from Percy's family. For example, a distant relative who has been corrupted by some dark magic. They might betray Percy for their own gain or because they are being controlled, and this betrayal could lead to Percy being killed.