Another possible antagonist could be a group of jealous demigods. They are envious of Percy's power and see the earthquake situation as a chance to get rid of him. They might try to frame him for the destruction caused by the earthquake and turn others against him, making it harder for him to deal with the actual disaster.
The gods could be the antagonists. They might see Percy's actions that led to the earthquake as a threat to their order and try to stop him, even if his intentions were good.
The plot could involve Percy accidentally triggering the huge earthquake while in a battle against powerful foes. Maybe his powers go out of control and the resulting earthquake shakes the very foundation of the fictional world he is in.
There could be a new, made - up character. This character could be a seer who had foreseen Percy causing the earthquake but was unable to prevent it. Now, this seer has to work with Percy to understand why it happened and how to prevent future disasters. Or it could be a young demigod who looks up to Percy and is now caught in the middle of the chaos Percy has caused and has to learn to be brave and helpful during this crisis.
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.
It could be the navy. They see pirates as outlaws and would be determined to capture Percy and his crew. They might have better - equipped ships and more trained soldiers, making them a formidable foe for Percy and his fellow pirates.
Monsters could also be antagonists. With Percy in a new, more powerful state as a godling, there could be new and more powerful monsters that are drawn to his power. These monsters might be stronger and more intelligent than the ones he faced as a demigod, and they could be after his godly essence or trying to use him for their own dark purposes.
It could be some of the other trainees who are jealous of Percy's progress and his special relationship with Chaos.
A powerful sorcerer who wants to use Percy for his own dark purposes could be an antagonist. This sorcerer might see Percy's unique abilities as a key to unlocking some sort of forbidden magic.
The gods could potentially be antagonists. If the pregnancy goes against some divine law or prophecy, they might try to interfere. For instance, Zeus could see it as a threat to the order of things and send his minions to cause trouble for Percy and Bianca.
It could be some powerful dark magic users. They are trying to take over the world, and Percy with his sniper is trying to stop them. They might have their own army of minions that Percy has to fight through.
The plot could involve Percy being tricked into using a powerful, ancient artifact that he doesn't fully understand. As he tries to figure out how to control it, it backfires and causes an earthquake. He then has to find a way to stop the destruction and reverse the effects of the earthquake while also dealing with the consequences of his actions, like the panic among the mortals and the possible damage to the demigod world.