A cool storyline could be that there's a memory - stealing monster in Camp Half - Blood. Percy is the first victim, and as he forgets who he is, he starts to act differently. His friends notice the change and realize something is wrong. They then search for a way to defeat the monster and restore Percy's memories. Along the way, they might have to face challenges like Percy unknowingly helping the monster or getting into dangerous situations because he doesn't remember his skills.
Another storyline might involve Percy getting lost in the Egyptian afterlife. He has to navigate through the different realms with the help of Egyptian gods such as Thoth, who is known for his wisdom. Along the way, he discovers secrets about the connection between the Greek and Egyptian pantheons. This could include how their powers are related and how the two mythologies might have influenced each other in ancient times.
Another storyline could involve her relationship with Percy Jackson. Maybe she has a bit of a rivalry at first because she's from Athena and he has his own heroic status. But then they end up having to team up against a common enemy, like a new powerful monster that neither could defeat alone. During this, they learn to respect each other's strengths.
One popular storyline could be Percy and Annabeth going on new adventures together, exploring different parts of the mythological world that weren't covered in the books. For example, they could travel to a long - forgotten island full of ancient and powerful magic.
One good storyline could be Percy and his friends getting thrown into the Marvel universe and seeking Tony Stark's help to get back home. Stark might be initially skeptical but then intrigued by their powers.
One interesting storyline could be Percy as a baby showing early signs of his demigod powers. Maybe he can control water in his crib, like making the bath water swirl around him in a mini - whirlpool. Another could be the reactions of the gods when they discover this new baby demigod. They might be worried about his potential or already planning how to use him in their future schemes.
There could also be a fanfiction where Percy has to face his inner demons in a more psychological way. Maybe he's haunted by the memories of all the battles he's fought and the friends he's lost. His friends then have to help him through this tough time, and in the process, they learn more about each other's deeper fears and insecurities.
One interesting storyline could be where Percy Jackson somehow ends up in Ariel's underwater world. Maybe he's on a quest that takes him there and he has to team up with Ariel to defeat a common enemy, like a sea monster that is threatening both the underwater kingdom and the surface world that Percy is from.
There could also be a fanfiction where the Hunters take in a new recruit who has a mysterious past. This new character might have powers that are unknown to the world of demigods and the Hunters have to figure out how to train and control these powers. Along the way, they discover that this new recruit is somehow connected to an old prophecy that could change the fate of the demigod world.
One interesting storyline could be a Futa Percy Jackson going on a new quest that involves saving a magical realm from an ancient evil. In this fanfiction, Percy's unique form might give her an edge in combat, like being able to use both male and female - like combat styles.
A really engaging storyline could be them being transported to a different era in the world of Greek mythology. They would have to adapt to the different rules and powers that exist in that time while still relying on their own abilities. This would put their friendship and skills to the test in a whole new and exciting way.