One possible plotline could be that Percy has been kidnapped by some mysterious enemy. Maybe it's a new villain who has a vendetta against him. His friends then start a search mission to find him, facing various challenges along the way.
Perhaps Percy discovers a dark secret about his past and decides to disappear on his own to protect his friends. He goes into hiding in a far - off place, but his friends suspect foul play and begin to look for him. As they search, they uncover more secrets about Percy and his family.
Well, he might disappear because of a powerful curse from an ancient enemy. Maybe he gets trapped in a different dimension. When he returns, he could have new powers or knowledge. For example, he might have learned some secret magic from the other dimension that helps him defeat a new threat in the Percy Jackson world.
Well, in some 'Hermione Disappears' fanfiction, it might be that she is targeted by a group of anti - Muggleborn wizards. They manage to make her vanish using some dark magic. Her friends, Harry and Ron, then start a frantic search. They might follow a series of mysterious clues she left behind before disappearing. It could also be that a time - traveling mishap causes her to disappear from the current timeline and she is stuck in another era.
One possible plotline could be that Ruby is kidnapped by a powerful new enemy. This enemy might be after her silver eyes power and plans to use it for some evil scheme. Another could be that Ruby accidentally gets transported to another dimension during a battle, leaving her team to search for her.
A plotline could involve Percy being bullied in a mortal school because he seems a bit odd. But then he discovers some ancient secrets that are somehow related to the world he should have been a part of as a demigod. He might start to find allies among some eccentric people who seem to know more about his true nature than he does, and together they uncover a mystery that bridges the mortal and the demigod world in an unexpected way. He has to constantly fight against the limitations of being a mortal while trying to figure out his place in a bigger picture.
Perhaps the horses are in some kind of danger or being mistreated, and Percy, being able to communicate with them, decides to be their savior. He could then embark on a journey to free them or find a better place for them. This would involve facing various antagonists who are against his mission. Along the way, he might also discover some secrets about the horses' origin or special powers that could further the plot.
One possible plotline could be that Luke has been corrupted by some dark force, and Percy has to fight him to save their world. Percy might be reluctant at first because they were once friends, but the greater good forces him into action.
One possible plotline could be Percy finding out he has cancer and having to deal with the reactions of his family. Some might be overly protective, while others might struggle to accept it. Another could be Percy supporting a family member with cancer, showing his growth and change from his more uptight self in the books.
It could be that Percy is made into a god but he doesn't fully understand what it means. He starts to notice changes in himself, not just in terms of power but also in his emotions and relationships. His mortal friends might start to fear or revere him in a way he doesn't like, and he has to find a balance between his new divine status and his old identity.
One possible plot could be that Percy is betrayed by one of his closest friends in Camp Half - Blood. Maybe Annabeth turns on him out of jealousy over his growing powers or a misunderstanding. Percy, feeling deeply hurt, decides to disappear into the mortal world. He cuts off all ties with the demigod community and tries to live a normal life, but his past keeps haunting him as monsters still sense his presence.
The gods are always a possibility. Zeus, for example, has been distrustful of Percy in the past. If Zeus feels that Percy is getting too powerful or is a threat to his rule, he could engineer a situation where Percy is betrayed. He might use other demigods or even mortals to turn against Percy.