A great plot idea could involve Percy finding out that there are other demigods like him, children of Rhea and an Olympian god. They form a secret group and together they must face a powerful enemy that is specifically targeting them because of their unique parentage. This could lead to Percy having to make difficult choices between loyalty to his new group, his Titan mother, and his Olympian father, as their interests may not always align.
One idea could be Percy discovering his connection to Rhea in a dream. Then, he starts to have strange powers related to her that he has to figure out how to control.
A plot idea might be that Percy is magically transported to a time when Poseidon and Hera had a major disagreement in the past. He has to use his wits and powers as Poseidon's son to prevent this rift from growing and causing chaos in the present. Also, he could be given a task by Hera to rescue one of her favored heroes who has been trapped by a sea monster under Poseidon's domain. This would put Percy in a tricky situation where he has to balance his loyalty to his father and the task given by Hera. He might also encounter a group of demigods who are descendants of both Poseidon and Hera in some way, and together they have to face a common enemy.
Maybe Percy discovers a prophecy that involves both his father Poseidon and Lupa. He has to journey to different realms under the sea and in the Roman wolf - related places. Along the way, he meets new demigods and creatures that either help or hinder him in fulfilling the prophecy.
One interesting plot idea could be Percy having to team up with a demigod child of Leto. They could go on a quest to find a long - lost artifact that has the power to restore balance between the sea and the moon's influence. Since Percy is the son of Poseidon, his control over water and the other demigod's connection to Leto's lunar powers would create a unique dynamic.
One interesting plot idea could be Percy having to deal with the conflicting natures of his 'parents'. Since Gaia represents the earth and Poseidon the sea, he might struggle with controlling both earth - related and sea - related powers. For example, when he's near a beach, he could accidentally cause small earthquakes or make strange things happen to the sea life. Another plot could involve Percy facing a threat that only his unique dual - heritage can defeat. Maybe an ancient evil that is both of the land and the sea, and Percy has to figure out how to combine his powers in a new way to stop it.
One idea could be Percy having to face a new and powerful sea monster that is awakened by an ancient curse. He'd have to use his powers in unique ways, maybe even discovering new abilities as the son of Poseidon. Another could be Percy traveling to a long - lost underwater civilization that has a connection to his heritage as an ancient son of Poseidon.
A great plot could be Percy getting into trouble in the mortal world and Poseidon having to come to his rescue without revealing his true identity to the mortals. This would create a lot of tension and interesting scenarios where Poseidon has to use his powers subtly. Also, they could be on a mission to save a group of sea creatures that are being hunted by an unknown and powerful force. Poseidon could be teaching Percy about the importance of all sea life along the way.
A cool plot could be Percy being sent on a quest that involves mending the rift between Zeus and Poseidon. Along the way, he meets old foes and new allies. He has to use his wits and the powers he got from his fathers to convince other gods and demigods to support his cause. For example, he might have to show the children of Zeus and Poseidon that they can work together instead of being rivals.
One idea could be Percy feeling betrayed by Poseidon and then finding a new family among other outcasts in the demigod world. He could form a group with them and go on adventures that are not related to Poseidon at all.
He would probably be a bit of an outcast at first. Since his parentage is so different, other demigods might be wary of him. But once they see his skills and powers, they would start to respect him. He might teach them some unique combat techniques he learned from his Titan mother Rhea, like different ways of using his powers in battle.