One interesting plotline could be Percy having to deal with the Slytherin values while still holding onto his own heroic nature from the Percy Jackson series. Maybe he has to face prejudice from some Hogwarts students who are suspicious of a 'half - blood' being the heir.
A possible plotline could be Percy's discovery of a hidden connection between the Greek gods and the magic in the wizarding world. As the heir of Slytherin, he might uncover secrets that were long forgotten. This could lead to a great adventure where he has to protect both the demigod and wizarding worlds from a common threat that is somehow related to this new - found connection.
One interesting plotline could be Percy discovering new powers related to his status as the heir of chaos. Maybe he can manipulate reality in unexpected ways, like creating temporary portals to different mythological realms. Another could be his relationships with other characters evolving. For example, his friendship with Annabeth might face new challenges as his new powers set him on a different path. He might also have to deal with new enemies who are after the power he holds as the heir of chaos.
Perhaps there could be a plot where Harry discovers ancient Slytherin magic that only the heir can access. This could lead to him having to make difficult choices between using this power for good or being corrupted by it. He may also have to deal with the Slytherin house's expectations of him as their heir, which are quite different from what he has known in Gryffindor.
Another plotline might involve Percy forming new alliances with other powerful beings in the chaos realm. He could be on a quest to gather ancient artifacts that are tied to the chaos powers, which would lead him to various mysterious and dangerous places. Along the way, he'd have to learn about the history and secrets of chaos, and how it all relates to his destiny as the heir. This would also involve a lot of character development as he struggles with the weight of his new role.
One interesting plotline could be the exploration of the true identity of the Heir of Slytherin. Maybe it's not who everyone suspects. For example, it could be a character who has been hiding their Slytherin heritage all along.
Draco Malfoy would be a likely character. Given his Slytherin status, he would likely have a complex relationship with Percy. He might start off as hostile, seeing Percy as an outsider, but then they could end up having to work together for some reason.
Well, one interesting plot could be the heir of Pontus having to deal with new and strange sea monsters that are loyal to Pontus. They might have unique powers and abilities that the heir has to figure out how to control or defeat. Another plot could involve a power struggle between the heir and other demigods who fear the power of Pontus. And sometimes, there are plots where the heir discovers long - lost secrets about Pontus' realm and has to protect them from falling into the wrong hands.
One interesting plotline could be the Seven facing a new, more powerful enemy that is a combination of different mythological creatures. This would test their teamwork and individual powers in new ways.
One interesting plotline could be Aphrodite taking a special interest in Percy for a quest related to love and beauty. Maybe she tasks him with finding a lost artifact that has the power to enhance or destroy love. Another could be Percy falling under a love spell cast by Aphrodite, which causes chaos among his friends as he starts acting out of character. And a third one might be Aphrodite using Percy as a pawn in a love - related game among the gods, where his actions and decisions have far - reaching consequences for the relationships between the deities.
One interesting plotline could be the siblings going on a secret quest together without the knowledge of Chiron or the other campers. They might face a new and unknown monster that tests their combined skills.
In some fanfictions, a centurion discovers a long - lost prophecy that involves Percy. This could lead to a race against time as they try to figure out the meaning of the prophecy and prevent a great disaster. Maybe it involves a new Titan rising and they need Percy's unique connection to the sea gods to stop it.