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.
Some ancient monsters that were once in love and had their hearts broken by Cupid's actions in the past could target Percy. For instance, a spurned nymph who was turned into a monster might seek revenge on Cupid's son. Also, there could be dark demigods who want to use Percy's powers for their own evil plans and when he refuses, they become his enemies.
Another potential enemy could be the followers of Eris, the goddess of discord. They would see Percy's role as a unifying force (through love) as a threat to their goals of creating chaos. So they might try to disrupt Percy's life, turn his friends against him, and generally make things difficult for him in the demigod world.
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.
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.
Annabeth could be a great ally. She's smart and resourceful, and she could help Percy figure out the mysteries related to Sobek and his Egyptian connections. Her knowledge of architecture and strategy would be useful in any quests Percy undertakes.
Annabeth could be a strong ally. She has always been there for Percy, and even though his parentage has changed, her loyalty might still hold. Grover too. He's Percy's best friend and would likely stand by him no matter what. Another potential ally could be the Hunters of Artemis. Since Diana is another name for Artemis, they might see Percy as someone they need to protect and help, especially if he is involved in something that concerns the goddess.
One idea could be Percy discovering new powers related to his heritage as Cupid's son. For example, he might have the ability to manipulate emotions on a grander scale, not just in terms of love. Another could be Percy getting involved in a conflict between the children of Cupid and other demigods who are suspicious of his newfound abilities.
Annabeth Chase might also be an ally. Her intelligence and strategic thinking could be valuable assets for the son of Hades. She could help him plan his moves, especially when dealing with the complex politics among the demigods and gods.
Annabeth could be one of his allies. Even though Percy is now the 'Son of Eris', their long - standing friendship and her loyalty might make her stand by him. She could help him understand his new situation and use her wisdom to navigate the challenges that come with it.
The centaurs from Camp Half - Blood could be allies. They are wise and have a long history of helping demigods. Their knowledge of ancient prophecies and combat techniques could be useful to the Son of Artemis. Additionally, some of the minor gods' children might side with him. For example, the children of Hecate could use their magic to help him in difficult situations. They might see the Son of Artemis as a symbol of change in the demigod world and want to support that. Nico di Angelo, with his powers over the Underworld, could also be an ally. He could offer protection from the darker forces that might target the Son of Artemis.
Annabeth would definitely be one of his top allies. She's been with Percy through many adventures and her intelligence would be crucial in helping Percy understand his connection to the creator and any new situations that arise. For example, she could research ancient texts to find clues about the creator's intentions for Percy.