In many fanfictions of this kind, Sally Jackson's character can be developed in unique ways. She may have to face challenges that test her loyalty and courage. For instance, she might be put in a situation where she has to choose between the safety of her loved ones and the greater good of the demigod community. This creates a lot of drama and tension, making the story very interesting. Also, her relationships with the gods could be explored, like whether she has a special connection with a particular god or goddess.
Probably Percy. Since he's her son in the original series, he would surely interact with her a lot in the fanfiction.
One interesting fanfiction could be about Sally's early adventures before Percy was born. It might explore her relationship with Poseidon in more depth. Another could focus on a day in the life of Sally and Percy when they have a special family event, like a reunion with other demigods at Camp Half - Blood. And there are also fanfictions that rewrite certain events from the original series with a different perspective from Sally's point of view.
One interesting story could be about a Japanese demigod who has a special power related to Japanese mythology, like the ability to control kami. They might team up with Percy Jackson on a quest that involves both Greek and Japanese mythological elements.
There could be fanfictions that focus on Sally and Poseidon's relationship in the context of Percy's adventures. Like when Percy is off on a quest, Sally and Poseidon might interact in ways that help or hinder Percy's journey. They could be working together behind the scenes to protect Percy, or there could be some sort of conflict between them that Percy has to eventually resolve.
Well, there's a fanfiction called 'Sally Jackson: The Hidden Years'. This story fills in the gaps of Sally's life when Percy wasn't around. It shows her dealing with the magical world on her own. Also, 'Sally's Magical Allies' is quite engaging. In this fanfic, Sally teams up with some unexpected allies from the world of gods and monsters. Then there's 'A Day in Sally's Life' which gives a detailed account of an ordinary day in Sally's life, but with a touch of the magical elements that surround her.
Another idea is to explore the relationship between the Norse gods and the Greek demigods in a fanfiction. Maybe the Norse gods are intrigued by Percy's powers and want to test him, or perhaps they offer him a quest in the Norse world. This could lead to Percy having to adapt to the different rules and challenges in the Norse realm.
A plot could be that Sally Jackson plants a lemon tree in her garden that turns out to be a gift from a minor goddess. The lemons from this tree have the power to give those who eat them the ability to see through illusions for a short time. Percy uses these lemons to his advantage when he is on a mission to retrieve a powerful artifact that is guarded by a monster that uses illusions to protect it.
One idea could be a story where Sally has a premonition about Percy's next big adventure and tries to secretly prepare him for it. Another could be a story set in an alternate universe where Sally has demigod powers herself and she teams up with Percy on a quest. Maybe a story where Sally gets transported into Percy's world at Camp Half - Blood and has to navigate the strange new environment while Percy protects her.
One idea could be that the forgotten demigod discovers a hidden power within themselves that is related to an ancient and forgotten god. This power could set them on a journey to find out more about their heritage and also put them in a position to save the demigod world from a new threat.
Perhaps Percy discovers a hidden prophecy that involves him sacrificing something dear to him to save the demigod world once and for all. This could lead to a lot of internal struggle as he decides what to do. In the fanfiction, he could journey to places never before explored in the original series to find answers.