One idea could be a fanfic where Sally has a special dream or vision involving Poseidon that gives her some hidden knowledge about Percy's future. For example, she might see a prophecy that only she can interpret and it leads her on a quest to find a lost artifact related to Percy's demi - god status.
A fanfic could explore the relationship between Sally and Poseidon before Percy was born. Maybe it delves into how they first met and the initial feelings they had for each other. It could be that Poseidon was drawn to Sally's kind heart and strong will, and Sally was intrigued by the mysterious god. This backstory could add depth to the overall Percy Jackson universe.
Another interesting fanfic concept could be that Sally has the ability to communicate with Poseidon in a way that no one else can. She uses this unique connection to plead with Poseidon to protect Percy during a particularly dangerous time. Poseidon, in turn, has to make some difficult decisions to balance his duties as a god and his feelings for Sally and Percy.
One idea could be a fanfic where Sally tells Percy stories about his father from her own perspective before he knew the truth. It would give a deeper look into their relationship and how Sally coped with the knowledge of Poseidon.
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.
A really interesting plot could involve her exploring a new part of the ocean that has been hidden for centuries. In this journey, she might encounter new sea deities that Poseidon has never mentioned. She could also find herself in a conflict between two groups of sea - creatures, and she has to use her wits and powers to bring peace. Along the way, she could learn more about her father's past and secrets that he has been keeping from her, which could change her relationship with him and her view of herself as a demigod.
One idea could be Sally and Poseidon having a secret adventure together that involves solving a mystery related to the sea. Maybe they discover a hidden underwater civilization that is in danger.
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 Percy having to face a new threat underwater that only Poseidon can help him understand. Maybe a lost civilization that Poseidon once had a connection with is now causing trouble. Another could be Percy going on a quest to find a powerful artifact that was once Poseidon's but has been stolen, and Poseidon gives him special powers or guidance along the way.
One idea could be Percy exploring an underwater realm that only Poseidon can access. He discovers ancient secrets about his father's past and the origin of his powers. Another could be a story where Percy has to team up with Poseidon to fight a new and powerful sea - born enemy. Maybe there's a prophecy that only their combined strength can fulfill.
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 Percy using his Poseidon powers to create a new underwater civilization. He could use his control over water to shape structures and gather resources, and his ability to communicate with sea creatures to bring different species together to form a unique society.
One idea could be Percy going on a quest that involves uncovering a long - lost secret about his connection to Poseidon that even the gods don't know. Maybe it's a hidden power that only surfaces when he faces a certain kind of threat. Another plot could be Percy having to deal with the jealousy of other demigods because of his special status as Poseidon's son. They might try to undermine him during a crucial mission, adding lots of drama and conflict.