His control over water could be used for building infrastructure. He could make sure there was a stable water supply for the growing city, which was crucial for its development. Also, his fighting skills and enhanced strength from being a demigod would make him a great leader in battles, protecting Rome from invaders.
One idea could be Percy using his water powers in new and unique ways to shape the early days of Rome. For example, he could use his control over water to create canals for trade or irrigation. Another could be Percy having to deal with the politics of Rome while also trying to hide his demigod nature. He might have to form alliances with certain Roman families while keeping his true identity a secret to avoid being persecuted.
Annabeth would likely be one of his main allies. She's smart and resourceful, and her knowledge of architecture and strategy would be useful in building and defending Rome. Also, Grover could be there. His ability to communicate with nature could help in various ways, like finding hidden passages or getting help from nature spirits.
One possible plot could be Percy Jackson having to navigate the complex politics of Rome as the King. He might face challenges from rival factions within the Roman demigod community who don't want an outsider like him in power. He could also be tasked with protecting Rome from new and powerful monsters that are specifically targeting the city because of his rule.
As Praetor, Percy could be involved in diplomatic relations within the Roman demigod community. He may have to make tough decisions about alliances and resource distribution. Also, his relationship with Annabeth might face new challenges due to the different Roman and Greek cultures. For example, there could be rules in the Roman camp that conflict with their relationship as it was in the Greek world. Fanfiction often explores how they overcome these cultural differences while Percy fulfills his duties as Praetor.
Perhaps the fanfiction could focus on Percy's relationships in his role as emperor. He could form alliances with other demigods in Rome. His relationship with Annabeth might also be affected. She could visit him in Rome and they could work together to solve problems, or there could be tension due to the differences between the Greek and Roman worlds.
Frank Zhang could also be an ally. He is a Roman demigod with shape - shifting abilities. His strength and loyalty would make him a valuable teammate for Percy. Additionally, Nico di Angelo, who has ties to both the Greek and Roman worlds, could be an important ally. His knowledge of the Underworld and his ability to shadow - travel could help Percy in various situations, whether it's getting information or quickly moving around in the Roman camp.
The Roman gods could be antagonists. Since Percy is a Greek demigod, they might not fully trust him as the King of Rome. They could try to undermine his rule, believing that he will favor the Greek side in any disputes or decisions regarding the demigod world.
Well, if Percy is the father of Zoe in fanfiction, it might mean that there are some hidden powers or abilities that Zoe could inherit from Percy. This could be a major plot point. Also, their relationship could be full of emotional turmoil. Percy, being the protective father, would have to deal with all the dangerous situations that Zoe gets into, just like he does with his other friends in the original stories.
Well, in this fanfiction, it could be that the author wanted to explore a different side of Percy's character. Being the 'Father of the Primordials' might mean he has the power to shape the very essence of the world in this fictional universe. It might also lead to some really interesting plot twists, like how he interacts with the existing gods and demigods, and how they react to his new - found status. It could also introduce new enemies or allies based on his role as the progenitor of the primordials.