Well, their relationships might become more complex. For example, Percy and Thalia might have a different dynamic as they see each other in a new light in the past. Since they are in a different time, they may rely on each other more for survival, which could strengthen their bond. Nico, being a bit of an outsider among them, might find himself more in tune with Percy and Thalia as they face the challenges of the past together. They may also form new relationships with people from the past, which could in turn affect their relationships with each other.
Their relationships could develop in many ways. At first, Percy and Thalia might have some friendly bickering as they used to, but with Nico there, they start to form a more united front. Nico, being a bit more withdrawn, might gradually open up to them more as they face challenges together. Percy could use his natural leadership skills to bring them together, and Thalia's fierce loyalty would make her a great ally for both of them. As they rely on each other more in the chaotic situations, their bonds would strengthen into deep friendships.
Their relationships would likely become more strained and cautious. Percy, who was always somewhat trusting, might become more guarded. Thalia could become more angry and vengeful, which might put a strain on her relationships with the others. Nico, already a bit of an outsider, might retreat further into himself. They would have to relearn how to trust each other, as the betrayal might make them question if there are any more secrets among them.
The main plot could revolve around fixing a mistake in the past that has led to a distortion in the present. For instance, something might have happened in the past that changed the balance between the different camps of demigods. Percy, Thalia and Nico go back to set things right. They'd encounter different cultural and technological aspects of the past time period. And they would likely face opposition from those in the past who don't understand their motives or are being influenced by the very thing they are trying to correct.
They could be like siblings. Percy and Thalia might act as the older siblings, protecting and guiding Nico. Percy, with his leadership skills, and Thalia, with her combat abilities, would be great at looking out for the younger Nico. They could also be like cousins, with a close - knit bond but still having their own individual family heritages that sometimes create interesting dynamics.
Percy and Nico might grow closer as they face new challenges together in Hogwarts. Thalia could initially be a bit of an outsider to their relationship but then gradually become more involved. Percy could act as a mediator between Nico and Thalia at times.
In highschool fanfiction, their relationships could develop in many ways. Percy and Nico could bond over their shared experiences of being different. Percy might help Nico come out of his shell and make more friends. Thalia would be like an older sister figure to both of them. She would protect them from any mean - spirited students. As time passes, they would have sleepovers at each other's houses (or cabins in Percy's case), and during these times, they would share stories and secrets, strengthening their relationships.
In this kind of fanfiction, they might face challenges adjusting to the new magical environment. Percy could be confused by the different types of magic in Hogwarts compared to his own demigod powers. Nico might struggle with the more structured and rule - bound nature of Hogwarts. Thalia could find it interesting but also be a bit rebellious against some of the Hogwarts traditions.
Percy would probably be very friendly and try to form study groups with the Hogwarts students. He's used to being a leader, so he might even start some new clubs. Thalia would be a bit more standoffish at first, but once she gets to know some students, she'd be very protective of them. Nico would be the mysterious one. The Hogwarts students might be a bit scared of him at first, but once they see his softer side, they'd become friends.
It's possible that there could be some strain on their relationships. The stress of being in a different time and the fear of changing things could cause arguments. Maybe they have different ideas about what they should do while in the past. For instance, Fred and George might want to have some fun and explore, while Harry is more focused on achieving a specific goal related to the future, which could lead to some friction between them.
His relationship with his father Poseidon would be different. He might see a side of Poseidon that he never knew before, like when Poseidon was younger and less experienced. This could change how Percy views his father and their connection.