It's possible that there are some jealous demigods behind it. They might see Percy as a threat to their own status or power. So, they made a deal with some evil forces to get Percy out of the way. Artemis's interference has now put her on their hit list too, and they will try to get rid of both Percy and Artemis to continue with their evil plans.
The antagonists could be some rogue scientists who are experimenting on demigods like Percy. They might be trying to harness the powers of the demigods for their own gain, whether it's for power, wealth, or some other self - serving reason.
It could be that Percy was in the laboratory because someone was trying to use his connection to the sea. After Artemis rescues him, they might seek help from Poseidon. Together, they could figure out a way to prevent those who captured Percy from using the sea's power for their own malicious purposes. Artemis could also use her skills in hunting and tracking to find out who was behind the plot against Percy.
Monsters are also common antagonists. For example, the Minotaur might be guarding the demigods. It's a fierce and well - known monster in Greek mythology, and it would be a formidable obstacle for Percy. Another could be the Hydra, with its multiple heads and regenerative abilities, making it a tough opponent when Percy is trying to reach the captured demigods.
One common antagonist could be an old enemy of Artemis who doesn't approve of her marrying Percy. This enemy might be a powerful Titan who sees their union as a threat to his plans for revenge against the gods.
It could be some rogue Titans who escaped from Tartarus. They want to cause chaos in Oklahoma and use Percy and Artemis to their advantage. Maybe they plan to capture them and use their powers to break free the other Titans.
The other gods might be antagonists. For example, Zeus could be against Artemis getting Percy back because he doesn't trust Percy or he has his own plans for Percy that don't align with Artemis'. Another god like Ares could also be an antagonist as he might see Percy as a threat and not want him to be on Artemis' side.
It could be some power - hungry shinobi within the Mist village. Maybe they see the clans as a threat to their own power and are trying to eliminate them or control them.
The Titans could be the main antagonists. Even though they have been defeated before, some of them might have found a way to return or their followers could be causing trouble. They see Artemis as a threat or a target for their revenge against the gods. Another possibility is a new group of powerful monsters that have banded together and are specifically targeting Artemis for her power and influence among the demigods.
A strict teacher could be an antagonist. Maybe this teacher has old - fashioned views and doesn't like Percy's unorthodox ways or Artemis's independent streak. The teacher could constantly give them detention or try to stop them from participating in certain school events that are important for the plot.
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.
In this fanfiction, the Titans could be the main antagonists. They might see Percy as a tool to use against Artemis. Since he's her son, they could try to manipulate him or turn him against her. Another possible antagonist could be the monsters that are drawn to Percy because of his unique heritage. They might sense his power and want to either destroy him or use him for their own evil purposes. Additionally, there could be a group of rogue demigods who are jealous of Percy's connection to Artemis and try to undermine him at every turn.