The plot might involve Percy trying to bring peace between Poseidon and Athena. There could be some ancient feud between them that Percy is determined to end. He could start by finding common ground between the two deities in their respective domains, like the sea and wisdom. Along the way, he would face many obstacles, including other gods and goddesses who don't want the peace to happen.
His relationships with other demigods would be very complex. For example, the children of Poseidon might see him as an oddity at first. They are used to their own set of powers and Percy having Athena's influence could make them a bit wary. On the other hand, the children of Athena might be skeptical of his loyalty as he also has Poseidon as a father. However, some demigods might be in awe of his unique heritage and look up to him, hoping to learn from his dual nature.
Another plot could involve Percy discovering a hidden connection between Poseidon and Athena that was long forgotten. This could lead to a situation where he has to convince the other demigods that this connection is important for the future of the camp. Maybe there are ancient prophecies that only he can understand due to his unique parentage.
A great plot could be Percy getting caught in a power struggle between Athena and Poseidon's followers. Since he is the son of both, he is a symbol of unity or a threat, depending on how different groups view him. He could be forced to prove his loyalty to both sides while also trying to maintain peace among them. This could involve battles, political intrigue, and lots of character development as he tries to figure out where he truly belongs in this complex world of gods and their followers.
Well, Percy's power over water from Poseidon and the wisdom and strategic thinking from Athena could lead to some amazing combinations. For instance, he could use water to create illusions, like mirages in a desert, but with a strategic twist. He could make the illusions in a way that confounds enemies and leads them into traps that he has planned out using Athena - like intelligence.
His character would likely be a blend of Athena's wisdom and Poseidon's boldness. He'd be more calculating in his actions, thinking several steps ahead like Athena, but also not afraid to take risks when necessary, similar to Poseidon. He might have a natural inclination towards both strategy and brute force, which could make him a very unpredictable and powerful character.
One common theme is family. Since Percy is the son of Poseidon and Amphitrite is Poseidon's wife, it often explores how Percy fits into this new family structure. Another theme is power. Percy already has his own powers from Poseidon, and Amphitrite being a goddess also has great power, so how their powers interact is often explored.
One interesting fanfic could be where Percy has to deal with the complex politics of having two powerful parents. He might struggle to find his place among the demigods who have more traditional parentage. For example, some might be jealous of his unique heritage, while others might fear his potential power.
A unique twist could be a love story between them, which is quite different from the normal perception of their relationship. Maybe they are reincarnated as mortals and fall in love without knowing their true divine identities at first. As they start to discover their powers and past lives, they have to deal with the conflict between their love and their roles as gods.
One possible plot could be a story of cooperation. Maybe there is a great threat to the world of the Greek gods, and Athena, with her wisdom, and Poseidon, with his power over the sea, have to work together. They could start off distrusting each other due to their past rivalries, like the competition for Athens. But as they face challenges, they gradually learn to respect and rely on one another's strengths.