To write a great highschool Percy Jackson fanfiction, start with a strong concept. Maybe it's Percy having to deal with a prophecy that involves his highschool. Develop your characters further. For instance, what if Annabeth is the valedictorian of the highschool? Build on the relationships between the characters in this new setting. Write engaging dialogue that reflects both the highschool and the Percy Jackson world. And most importantly, have fun with it and don't worry too much about making it perfect at first. Just keep writing and refining your story.
When writing your highschool Percy Jackson fanfiction, you need to keep the voices of the characters true to the original. Percy is sarcastic and brave, so make sure he acts that way. For the highschool part, add in elements like cliques, school events, and teachers. You can also introduce new conflicts that are relevant to highschool life, such as getting into a good college or dealing with a bully who has a secret connection to the mythological world. Also, don't be afraid to let your creativity run wild with new monsters or magical items.
First, know the Percy Jackson universe well. Read the original books thoroughly to understand the characters, their powers, and the rules of the world. Then, think about a unique highschool setting. It could be a highschool just for demigods or a normal highschool where Percy has to hide his identity. Plan out your plot, whether it's a new adventure, a love story, or a mystery.