In this fanfiction, some of the Titans or other powerful ancient beings that want to disrupt the balance further could be his enemies. They might try to use Percy's rogue status to their advantage, but Percy might not want to be part of their plans. So, they could turn on him and try to eliminate him to prevent him from interfering with their own evil designs.
Some of the more traditional and rule - following demigod groups at Camp Half - Blood could be against him. They believe in following the established ways and Percy's rogue behavior goes against that. They might see him as a troublemaker and try to bring him back to the 'right' path.
In this fanfiction, Percy might decide to break away from Camp Half - Blood. He could start exploring the mortal world on his own terms, using his demigod powers in ways that the camp rules don't allow. Maybe he teams up with some unexpected allies, like a group of outcast demigods or even some friendly monsters.
He could meet some Aboriginal heroes or spirits. They might have their own powers and knowledge that Percy can learn from.
Well, sometimes in fanfiction, his brother might be a mortal who discovers his demigod heritage later. This could add an interesting twist to the story as he has to adapt to the world of gods and monsters. Or it could be a long - lost half - brother from a different camp, like a son of Poseidon from another part of the world who was hidden away for some reason.
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.
The Titans could be potential enemies. Even though they've been defeated before, some of them might be resentful and see Percy as the Chaos Champion as a new threat to their possible plans of a comeback. Kronos, for example, might have some of his essence lingering and try to possess other powerful beings to go against Percy.
The new enemies could be the descendants of an ancient and forgotten race of sea - dwelling creatures who are jealous of Percy's growing power. They might see him as a threat to their long - lost dominion over the oceans. Another possibility is a group of rogue demigods who have been corrupted by dark magic and want to steal Percy's new powers for themselves. There could also be a powerful sorcerer from a far - off land who has heard of Percy's powers and wants to use them to break a curse that has been placed on him.
The children of Ares might see Percy as a threat. Since Cupid represents love and Ares represents war, their natures are quite opposite. The Ares kids could be jealous of Percy's powers or simply not trust him because of his different lineage.
The traditional enemies of the demigods, like the Titans or the Giants, could still be his enemies. They might see him as an abomination because of his father being Charon. Also, some of the more puritanical demigods who follow the Olympian gods strictly might oppose him.
The Titans could still be a threat. Even though they were mostly defeated, there could be some remnants or new Titans emerging. For example, a Titan who was in hiding and now sees Percy as a threat to his plans of taking over again.
He might meet some talented witches and wizards. Maybe there would be a student who is an expert in magical beasts and they could share stories about their encounters with strange creatures.