One interesting plot could be Percy and his friends having to solve a mystery within Westover Hall that involves an ancient artifact hidden there. Maybe it's a lost weapon of a Greek god that has the power to control the weather. Another plot could be a new character arriving at Westover Hall who is secretly a demigod in disguise, and Percy has to figure out their true identity before a monster attacks. And there could also be a plot where the school is hosting a competition, but it's secretly a test by the gods to see which demigod is the bravest and most worthy.
Some plots could be centered around the idea that there's a prophecy related to Westover Hall. For example, it could be foretold that a great battle will take place there between the forces of good and evil, with Percy being a key figure. Also, a plot could involve a teacher at Westover Hall who is actually a minor god in disguise, and Percy has to figure out which one and why they are there. Additionally, what if there's a hidden underground chamber beneath Westover Hall filled with treasures and traps, and Percy and his friends are on a quest to explore it.
There might be a fanfiction where an older Percy Jackson goes to Westover Hall undercover to investigate some strange magical occurrences. He teams up with some of the students who have a latent magical ability. In this story, he has to hide his identity while trying to figure out what's going on. The author could play with the idea of Percy using his skills in a more mature and strategic way compared to when he was younger.
One idea could be that Percy discovers an ancient immortality spell hidden in the depths of Westover Hall. He has to face off against some dark forces that also want the spell for their own evil purposes. Maybe he teams up with some new friends he makes at the hall to keep the spell out of the wrong hands.
Well, in this fanfiction, Percy's immortality could lead to some really interesting character development. He may start to feel lonely as he realizes that he will outlive all of his friends. This could cause him to be more withdrawn at first. But then, as he interacts with the students at Westover Hall, he might find new meaning in his immortality. He could start to see it as a way to protect others not just for a short time, but for as long as he exists. He could also form deep and lasting friendships with those who accept him for who he is, regardless of his immortality.
Percy himself is always an intriguing character to include. His sarcastic humor and his ability to get into trouble and out of it are fun to write about. Annabeth is also great. Her intelligence and her strategic mind can add a lot to the story. Grover is another one. His loyalty and his goat - like tendencies can create some humorous and heartwarming moments. And don't forget about the villains. A well - written villain like a powerful monster or a devious demigod who has a vendetta against Percy can make the story really exciting.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). They have a large collection of Percy Jackson fanfictions, and you can use the search function to specifically look for ones related to older Percy and Westover Hall. Just type in 'older Percy Jackson Westover Hall' in the search bar.
One interesting plot could be Percy having to face an alternate version of himself that has turned evil due to some dark magic. This would create a great internal conflict as he battles not only an external foe but also his own dark side.
One interesting plot could be Percy and his friends going on a quest in a new, unknown realm. Maybe a place that's not part of the regular Greek mythology but still related in some way.
Another plot might be a scenario where Percy tries to reason with Kronos. He could attempt to understand Kronos' motives for wanting to destroy the Olympians and find a compromise. This would be a complex and emotional journey as Percy has to face the being who nearly destroyed his world.
One interesting plot could be where the NPU (assuming it's some new power or entity in the Percy Jackson universe) is a key to unlocking an ancient prophecy that no one knew existed. Percy and his friends have to figure out how to use the NPU to their advantage while also dealing with the usual monsters and gods trying to stop them.
A cool plot could be a time - travel fanfiction. The Minotaur travels back in time to the era when the gods were more actively involved in the mortal world. He could interact with the gods, and Percy has to follow him through time to stop him from causing chaos. This would involve Percy having to deal with different rules and powers in the past, and also understanding the Minotaur's motives for going back in time.