One possible storyline could be that Percy sacrifices himself to save his friends and the entire demigod world from a powerful new threat, like an ancient primordial god awakened. His death could then lead to a new era where his friends are inspired by his selfless act and strive to keep the peace in his memory.
In some fanfictions, Percy could die in a battle against a horde of powerful monsters. His death might be the catalyst for a change in the relationship between the gods and demigods. Since Percy was always a bridge between them, his death could make the gods realize they need to be more involved in protecting the demigods, and his friends could start a revolution of sorts to demand better protection from the gods.
In a fanfiction, Percy could lose an eye while on a quest. Perhaps he's exploring an ancient, cursed temple. There are hidden traps everywhere, and as he's trying to solve a riddle to progress, one of the booby traps activates. A sharp blade swings out and hits his eye. This event could change his relationships. Some friends might be overly protective, while others might not know how to act around him. Percy would then have to prove that he's still the same hero, just with a new challenge to overcome.
One possible storyline could be Percy leading a Titan rebellion against the Olympians. Since he has a connection to the Olympian side as well, it would create a very interesting internal conflict for him.
One possible storyline could be Percy forming a band with his demigod friends. They could go on a tour across different mythical realms, performing for gods and monsters alike.
Perhaps Percy is a single dad because his partner was lost in a battle against the Titans or some other great evil. In the fanfiction, he could be dealing with the grief of that loss while still being a great father. He might take his child on adventures around the places he used to go as a teen demigod, like the Labyrinth, but this time it's to teach his child about their heritage and how to survive in a world full of mythological threats.
One possible storyline could be Percy losing hope after a major betrayal by a close friend in the demigod world. Maybe he feels like he can't trust anyone anymore and starts to isolate himself from his usual group. This could lead to a downward spiral where he even questions his own abilities and purpose.
One possible storyline could be the OC being a new demigod who catches the attention of both Percy and Artemis. Maybe the OC has a special power that is crucial in a new threat that's emerging in the world of the gods. For example, the OC could have the power to control time briefly, which becomes important when an ancient enemy tries to rewrite history to gain power.
Another storyline could involve Percy using his water - based powers in new and unique ways within the Roman military context. Since the Romans have different views on the gods and their powers compared to the Greeks, Percy might face challenges or opportunities when it comes to revealing and using his abilities. He could be seen as either a great asset or a potential threat.
One possible storyline could be that in a battle against a new and powerful enemy, Annabeth sacrifices herself to save Percy. Maybe she steps in front of a deadly attack meant for him, like a powerful magic blast from a primordial being. This would shatter Percy, leading him on a journey of both revenge and self - discovery as he tries to come to terms with her loss.
In some fanfictions, the storyline might involve a mix - up of magic. Percy's powers from the Greek gods could be pitted against the dark magic of Voldemort's heir. For example, Percy's ability to control water might be used to counter the heir's fire - based dark spells. There could also be a storyline where Percy is sent into the wizarding world by the gods to stop the rise of Voldemort's heir because they fear the chaos it could bring to the entire multiverse. And of course, there could be a love story where a character from Percy's world falls in love with someone related to Voldemort's heir, creating a complex web of relationships.
One possible storyline could be that Hera, in her complex and often manipulative way, sees something unique in Percy. Maybe she decides to use Percy for a quest that is crucial to maintaining the balance in the Olympian world. Percy, at first reluctant, eventually gets drawn into it because of his sense of duty. Another could be a more emotional storyline where Hera, who is often seen as cold, has a moment of vulnerability and Percy, with his empathetic nature, is the only one who can understand her. This could lead to an unlikely friendship or a mutual respect that no one expected.