One possibility in a 'Percy is thrown back in time' fanfiction is that Percy gets to train his younger self. He could pass on all the skills and knowledge he has gained over the years. This would make his younger self much more powerful and capable at a younger age. He might also be able to influence the decisions his younger self makes, leading to a completely different path for his life and the world around him.
Well, Percy could end up changing the entire course of history in the 'Percy is thrown back in time' fanfiction. He might accidentally stop some important relationships from forming or start new ones that were never meant to be. Also, he could have a chance to see his loved ones who are no longer alive in his original time, which would be an emotional rollercoaster for him.
Percy might run into his old friends' ancestors. This could create some really strange and exciting interactions. For instance, if he meets an ancestor of Annabeth, he could learn things about her family history that she doesn't even know.
He could potentially change some events in the past that had a big impact on his present life. Say, he could prevent some of the early attacks by monsters that made his life so difficult growing up. This would completely alter the course of his life and the lives of those around him. It's a really cool concept to think about how one small change in the past could have a huge ripple effect in the future.
In such a fanfiction, Percy might use his knowledge of the future to change some key events in the past. For example, he could prevent some of the earlier disasters or conflicts in the Percy Jackson universe. Maybe he'd try to stop the first encounter with a certain monster in a different way to avoid the chaos it caused.
Maybe they would meet their ancestors. Percy could see his Greek hero predecessors and Artemis might interact with the first hunters she ever had. This could lead to some interesting exchanges, like learning forgotten hunting techniques or ancient combat skills.
He could meet his parents when they were young. Maybe he'd get to see his mother before she met his father and understand more about her life back then.
In the 'Percy goes back in time fanfic', he may also meet his younger self. This could lead to some really interesting and confusing situations. He would have to be careful not to disrupt the timeline too much while still achieving whatever his goal is for going back in time.
Perhaps Percy will discover secrets about his family or his powers that were previously unknown. Since he's in the past, there could be ancient magic or knowledge that he stumbles upon. This newfound knowledge could give him an edge when he returns to his own time, if he ever does. He might also face challenges like trying to blend in with the people of the past, as his modern ways could make him stand out and cause suspicion.
One idea could be Percy going back in time to the era of the first Olympian gods and having to deal with the raw, unbridled power of those early deities. He might find himself in the middle of a power struggle between Zeus and his father, Kronos, before the Titanomachy. Another plot could involve Percy trying to prevent a major disaster in the past that has far - reaching consequences in his own time. For example, stopping the release of a powerful monster that was supposed to be sealed away long ago.
In this fanfiction, Percy might struggle to catch up with the school work he missed. There could also be some sort of rivalry or conflict with a new student. And perhaps he'll discover a hidden part of the school that has some special significance related to his past adventures.
Perhaps Percy goes back to Goode to find a sense of normalcy. He might try to participate in school activities like sports or clubs. However, his past as a demigod will surely follow him. His powers could accidentally surface during a school event, causing chaos and confusion among his classmates. He'd then have to figure out how to cover it up while also protecting those around him from any potential danger.