Some ancient and powerful monsters could be antagonists. Since Percy is now connected to the Fates, any disruption in the natural order might attract these monsters. They could see the situation as a chance to gain power or revenge. For instance, a powerful Titan who was once imprisoned might see Percy's new status as a way to get back at the gods by attacking him.
There could be a group of rogue demigods as antagonists. They might envy Percy's position and think that he is misusing his power as the husband of the Fates. They could try to steal his power or get him out of the way so that they can have a say in the Fates' decisions.
A group of powerful and corrupted demigods could also serve as antagonists. They might have been promised great power by some dark force if they can disrupt the work of the Fates. So they set out to target Percy and try to stop him from fulfilling his role as the God of Fates.
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.
Well, perhaps a plot where Percy discovers that being married to the Fates gives him the ability to see snippets of the future, but it's all jumbled up. He then has to work with the Fates to figure out how to use this new power properly. Also, there could be a story line where other gods are jealous of Percy's connection to the Fates through marriage and try to undermine him.
The main antagonists could be some old enemies of Percy or Reyna who don't want to see them happy. For example, a vengeful monster from Percy's past might try to disrupt their relationship. Maybe it's a Titan who was once defeated by Percy and wants to ruin his newfound happiness with Reyna.
Well, without having read it, it could potentially be about Percy getting caught up in the plans or manipulations of the Fates. Maybe there are some adventures or challenges that Percy has to face due to their influence. The 'lemon' part might imply some sort of sour or difficult situation he gets into because of the Fates.
It could be the traditional villains from the original story, like the Titans or some powerful monsters. They might torture Percy to get information or just to cause chaos.
It could be an old enemy from Greek mythology that has been resurrected. For example, a powerful Titan who has a vendetta against the demigods, especially Percy and Annabeth.
Percy could develop a greater sense of purpose. Since he is the son of the Fates, he might start to see the grander scheme of things more clearly. He could become more solemn and less impulsive as he realizes the weight of the Fates' plans on his shoulders.
First, try Archive of Our Own. It's known for its extensive library of fanfictions. FanFiction.net is also a classic site for finding various fan works. Additionally, if you're part of any Percy Jackson fan forums, post a query there. Some fans might be able to point you to the exact location of this 'percy and the fates lemon fanfiction'. There are also some smaller, niche fanfiction archives that might have it, but they might be a bit harder to find.
Obviously, Percy Jackson is the main character. But there could also be Annabeth Chase, his long - time friend and love interest. Grover, his satyr friend, might also play an important role. And since it's related to the Fates, the three Fates themselves - Clotho, Lachesis, and Atropos - could make appearances, either as allies or antagonists depending on the story.