Percy's powers of navigation might be enhanced. Atlantis was a center of knowledge, and being born there could have given him access to ancient maps or a natural sense of direction in the ocean. Maybe he can find hidden places in the sea more easily. Also, his ability to resist the pressure of the deep sea could be much greater than other demigods. This would allow him to explore deeper parts of the ocean where no one else has been, and find all sorts of treasures or secrets.
His water - related abilities could be stronger. Since Atlantis was an underwater city, he might have an even deeper connection to the water. He could control water in ways that other demigods can't, like being able to communicate with sea creatures more effectively.
If Percy Jackson were a vampire in a fanfiction, he might retain his water - controlling abilities from being a demigod. His vampire strength could be combined with his natural athleticism, making him an even more formidable fighter. He could use his speed to quickly reach bodies of water to enhance his powers, and his vampire senses might help him detect threats in the water as well.
Well, it could involve Percy having a unique connection to the lost city. Maybe he discovers some ancient powers there that are tied to Atlantis' history. He could meet Atlantean characters who have been waiting for his arrival, thinking he's some sort of prophesied hero.
His powers could be more nature - based. For example, instead of just controlling water, he might be able to control all forms of liquid in nature, like sap or blood. His connection to the wild could also make him more attuned to the emotions of animals, allowing him to communicate with them more effectively.
Well, in a fanfiction where Percy is born in Greece, his powers would likely have a more 'Greek - flavoured' aspect. Since he's in the homeland of the Greek gods, his connection to water could be intertwined with the Greek concept of the four elements. So, his water powers might interact more with the other elements in a way that is more in line with Greek elemental theory. He might also be able to draw on the power of Greek water deities more directly, which could enhance his abilities and give him new ways to use his powers in battles and other situations.
His relationship with Annabeth would be very different. Instead of their usual dynamic on land, they'd have to figure out how to interact in the water. Annabeth might have to learn to trust Percy in his new form, and Percy would have to deal with any insecurities about his merman self. Their relationship could become more strained as they adjust, or it could grow stronger as they face new challenges together.
Well, if Percy Jackson was born a Roman in fanfiction, his whole upbringing would be different. He'd be trained in the Roman way of fighting and thinking. Maybe he'd be more disciplined from the start, as the Roman camp is big on that. He'd also have different relationships with the gods. Instead of the more laid - back Greek god interactions, he'd have to deal with the more formal Roman ones.
Percy might also become a bit more self - aware. When he sees how different he can be in other universes, he will start to think more about his own identity. He may realize some of his own strengths and weaknesses that he hadn't fully recognized before. And this new self - awareness could help him grow as a character and a hero.
His ability to communicate with sea creatures might seem strange for football, but what if there are some sort of water - based spirits in the stadium's plumbing? He could get some 'inside information' about the field conditions or even use them to spook the opposing team. Also, his enhanced strength as a demigod would surely make him a force to be reckoned with when it comes to tackling or blocking.
Well, it could make him more complex. Absorbing abilities might give him new outlooks and skills that change how he views himself and his place in the world. For example, if he absorbs a strategic ability, he might become more of a planner rather than relying on his usual impulsive nature. This could lead to him being more respected by his peers and also give him new internal conflicts as he tries to balance his old self with the new capabilities.
His upbringing in Atlantis might make Percy more in - tune with the ancient and mystical side of the ocean. He would grow up surrounded by Atlantean lore and history. This could give him a sense of wisdom and mystery that he wouldn't have if he was raised on the surface. He might be more solemn and less likely to engage in the typical teenage banter that he does in the original stories.