Who could be the main antagonists in a 'Percy Jackson adopted son of Pontus' fanfiction?

The other gods might be antagonists. Since Percy is the son of Gaea and Pontus, the Olympian gods could see him as a threat. They might be worried that he'll side with his primordial parents and disrupt the balance they've been trying to maintain. So, they could send their demigod children or even some minor gods to oppose Percy.

Well, it could be about Percy having to deal with the powers and heritage that come with being the adopted son of Pontus. Maybe he discovers new underwater abilities that are different from his Poseidon - given powers. He might also have to face enemies who are after the secrets Pontus has.

The Titans could still be antagonists. Even though Percy is now associated with Artemis, the Titans might see him as a threat or a tool to use against the gods. Kronos, for example, could try to turn Percy to his side by offering him power or by threatening those he cares about in Artemis's group.

The Olympian gods could be the main antagonists. Since Percy is the adopted son of Kronos, they might see him as a potential threat and try to stop him before he can fulfill any of Kronos' possible plans. They may send their demigod heroes after him.

Another god could be the antagonist. For instance, Hades might be jealous of Demeter's newfound 'son' and the attention Percy is getting. He could send his minions to cause trouble for Percy or try to undermine Demeter's influence on Percy, leading to a series of battles and challenges for Percy to overcome.

The Titans could be antagonists. Since Nyx is an ancient and powerful goddess, the Titans might see Percy as a threat because of his connection to her. They could try to either turn him against Nyx or simply eliminate him.

Hera could be a main antagonist. Since she's often jealous and protective of Zeus, she might not be happy with Percy being adopted. She could try to undermine him at every turn. Another could be Ares. He might see Percy as a threat, especially if Percy starts to gain more power as Zeus' adopted son.

Some of the traditional sea monsters like the Kraken could be antagonists. Since Percy is now in a more prominent position in the sea world as Amphitrite's adopted son, the Kraken might see him as a threat and try to attack him.

Another possibility could be a group of rogue demigods who are against any form of association with the underworld. They view Percy's new identity as something dark and evil. They form a group to oppose Percy and try to drive him out of the demigod community. They might even try to frame him for crimes he didn't commit in order to get the other demigods to turn against him.

Another possible antagonist could be some of the more power - hungry and jealous demigods. They might not like that Percy has been adopted by Apollo and is getting special attention. They could try to sabotage his missions or spread rumors about him to turn the other demigods against him.