There could also be various sea creatures that are personified and play significant roles. For example, a mermaid or a sea - horse - like creature that acts as Percy's guide through the complex underwater world of Atlantis. And don't forget the gods and goddesses who still have influence over Atlantis. Poseidon himself might make an appearance to guide or test Percy in this new setting.
Often, Percy's friends from Camp Half - Blood like Annabeth might also be involved. Annabeth could provide her wisdom and strategic thinking to help Percy navigate the political and magical challenges in Atlantis. Grover might also pop up in some way, perhaps using his connection with nature to communicate with the unique plant - like life forms in Atlantis.
Obviously, Percy Jackson is one of the main characters. He is the son of Poseidon and has his own set of powers and a strong sense of justice. Another important character could be the current prince or princess of Atlantis. They might be Percy's ally or rival, depending on the story.
One interesting plot could be Percy exploring the hidden, ancient parts of Atlantis that are full of forgotten magic and powerful artifacts. Maybe he discovers a long - lost prophecy that only he can fulfill, which involves uniting different sea - based tribes in Atlantis.
The Titans could still be a major threat. Even though they were mostly defeated in the original series, some of their followers might see Percy's new role in Atlantis as a threat to their plans for chaos. They could try to undermine Percy's position in Atlantis and use the underwater city as a base for a new uprising.
It could be a power - hungry Atlantean noble who wants to rule not just Atlantis but also the surface world. He sees Percy as a threat to his plans and tries to stop him at every turn.
Grover can also be a great character in these fanfictions. His friendship with Percy is always a key element. When Percy becomes a prince, Grover might be the one to keep him grounded and remind him of his roots. He could also be involved in some comical situations as he tries to adjust to Percy's new royal lifestyle, like accidentally causing a scene at a grand ball or getting lost in a huge royal palace.
He might discover new sea creatures that are unique to Atlantis. Maybe he'll find a hidden school of magic there, or encounter ancient sea gods who have been forgotten by the outside world.
The main villain could be a power - hungry Atlantean sorcerer who wants to use the power of Atlantis to rule both the underwater world and the surface. He might see Percy as a threat to his plans and try to eliminate him.
One idea could be Percy having to face a new underwater threat that is specifically targeting Atlantis. Maybe a powerful sea monster that was once imprisoned by the Atlanteans has been released and Percy has to figure out a way to stop it without causing too much destruction to the underwater city.
Obviously, Harry Potter would be one of the main characters. And there would probably be some Atlantian characters like the King or Queen of Atlantis, or other important Atlantian figures. Maybe some of Harry's friends from Hogwarts could also be involved, like Hermione and Ron, if they also get dragged into the Atlantis adventure.
Well, he might have a whole different set of skills. Maybe he'd be an expert at underwater magic that's unique to Atlantis. He could have friends among the Atlantean creatures and be more in tune with the ocean's secrets there than in the regular Percy Jackson stories.
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.