He would likely be more in tune with the earth and the sky elements. His powers might not just be limited to water control as before. For instance, he could have the ability to manipulate the ground like Gaia's children and also have some control over the air or weather like related to Ouranos.
One idea could be Percy having to deal with the conflicting powers within him from being the son of Gaia and Ouranos. Maybe he discovers a hidden realm that only he can access due to his unique parentage.
One idea could be Percy having to deal with the ancient powers within him from Ouranos and Gaia. For example, he might have the ability to control the very fabric of the earth and sky in ways not seen before. He could use the power of Ouranos to manipulate the weather on a grand scale and Gaia's power to reshape the land during battles. Another plot idea could be Percy being hunted by both the gods and primordial forces who fear his combined heritage. This would lead to him constantly being on the run and having to form new alliances with unlikely characters.
In most traditional Percy Jackson lore, he is the son of Poseidon. However, in fanfiction, authors can create all kinds of alternate universes. So, it's possible for him to be depicted as the son of Gaia and Tartarus in some fan - created stories.
His relationship with Annabeth would likely be more complex. She might be both in awe and a bit fearful of his new powers. Percy, being the son of such powerful primordial beings, could start to seem more distant to her as he delves deeper into understanding his heritage. With the other demigods, they might either look up to him as a powerful figure or be jealous of his new - found status. Some might even be suspicious of his intentions, fearing that he could side with the primordial forces against the Olympians.
One possible plot could be Percy's discovery of his true parentage. He might struggle with the implications of being the son of two powerful primordial deities. For example, he could face a conflict between the forces associated with Ouranos and Gaea. This could lead to him having to make difficult choices about which side to support, if any. And he may also have to deal with the reactions of his friends and the other demigods who might view him differently now.
Maybe there's a plot where Percy has to team up with other demigods who also have primordial roots. Together, they have to face a great evil that is threatening to destroy the balance between the primordial and Olympian worlds. They would have to use their combined powers and knowledge to save both worlds.
It could involve Percy having new and powerful abilities. Since Ouranos is a primordial god, Percy might have control over fundamental elements like the sky or the very essence of creation. For example, he could be able to manipulate the air in ways he couldn't before, like creating powerful storms or even pockets of different atmospheres.
Percy Jackson is the main focus, of course. However, in fanfiction, we often see the introduction of characters from different mythologies. So, there could be characters from Roman mythology interacting with Percy. Additionally, there might be some minor characters from the original Percy Jackson series who get more development in the fanfiction. For instance, Nico di Angelo could have a bigger role, maybe helping Percy understand his new powers as the Son of Gaia, or even having some sort of power struggle with him.
One possibility is that Percy's new status as the adopted son of Ouranos gives him unique powers. He might be able to control primordial elements like the very essence of the sky and space. For example, he could create storms on a much larger scale than before, drawing power from the origin of the heavens. Another aspect could be his relationship with the other gods. They might view him with a new level of respect or fear, which would change the power dynamics in the demigod world. And Percy would also have to deal with the expectations and responsibilities that come with being related to such a powerful primordial being.