Another possible antagonist could be some of the more bloodthirsty and power - hungry warlords or demons in the God of War universe. They might not care about Percy's origin or his powers, but simply see him as someone to be defeated or enslaved. These types of characters are often driven by pure greed and a desire for chaos, which would put them directly in Percy's path.
It could be really exciting. Percy might use his water - controlling powers in the God of War universe. He could face off against the fearsome creatures from God of War like the Minotaur in a whole new way. Maybe he'd team up with Kratos and use his quick - thinking and strategic skills along with Kratos' brute strength.
Maybe some of the more malevolent Greek gods could be antagonists. If Naruto's presence disrupts the balance of power among the gods, some of the jealous or power - hungry ones could try to get rid of him. For example, Hades might see Naruto as a threat to his domain and try to stop him from interfering in the affairs of the underworld.
The Titans related to chaos and destruction of nature could be great antagonists. For example, Cronus might want to use Percy's newfound power as the God of Nature to further his own dark plans.
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.
Maybe some of the more vengeful gods could be antagonists. For example, if Hera doesn't like Percy's decision to adopt Thalia, she could send various challenges their way. Also, there could be some ancient monsters that are awakened by Thalia's presence, and they would want to destroy her. These monsters could be sent by some minor gods who are jealous of the attention Thalia might get from the major gods.
A group of rogue demigods could also be antagonists. These demigods might be jealous of Percy's status and Bianca's unique abilities. They could form a sort of anti - hero group that tries to undermine Percy and Bianca's quests and cause trouble for them. For example, they might steal important items that Percy and Bianca need for their mission.
A group of ancient spirits of chaos that have been awakened by the imbalance in natural disasters could be the antagonists. They thrive on destruction and see Percy as a threat to their plans of creating total chaos. They would constantly try to undermine Percy's efforts to control and prevent disasters, and they might possess other powerful beings to fight against him.
Obviously, the God of Death could be a main antagonist if he has some malicious plan. He might be trying to tip the balance of life and death in his favor, causing chaos in the mortal and demigod worlds.
The Titans could be great antagonists. They might see Percy as a threat to their power if he becomes the God of Elements. Kronos, for example, could try to steal Percy's newfound elemental powers to regain his full strength and take over the world again.
One possible antagonist could be Kronos again. Since Percy now has time - related powers, Kronos might see this as an opportunity to use Percy to his advantage. He could try to manipulate Percy into changing the past in a way that would free him from his eternal prison. Another could be a new, unknown deity who is jealous of Percy's newfound power over time and space and wants to take it for himself.