Maybe Percy gets lost in a forest and a kind Naiad guides him out. Along the way, they have to face some mythical creatures together and form a strong bond. This could lead to a series of adventures where the Naiad becomes an important ally to Percy in future quests.
One idea could be Percy helping a Naiad protect her water source from pollution. He uses his demigod powers to fight off the forces causing the pollution.
It's possible. There could be other demigods or mythical creatures. Maybe a centaur who gives Percy some advice regarding the naiads. Or a sea monster that they have to face together.
I'm not sure specifically as I haven't read this particular fanfiction. But it might involve Percy having some sort of adventure or encounter with the naiads. Maybe they go on a quest together or there's some mystery in the underwater world that they have to solve.
In some fanfictions, Grover, Percy's satyr friend, might also be an important character. He could accompany Percy when he encounters the Naiads. And there could be a particular Naiad that stands out more than the others, perhaps one with a unique personality or special powers. For example, a Naiad who has the ability to control not just water but also the plants around her water source.
One idea could be that Percy is framed for stealing a powerful magical artifact. His friends initially doubt him, but as he tries to prove his innocence, he uncovers a conspiracy within the magical community. For example, a secret group wants to use the situation to gain more power and is setting him up as a scapegoat.
One idea could be that Percy has to seek Athena's wisdom to solve a complex mystery in the mortal world that is somehow related to the gods' ancient secrets. Maybe it involves a powerful artifact that was lost long ago and only Athena's knowledge can lead Percy to it.
One idea could be Percy joining the hunt temporarily. Maybe there's a prophecy that requires his unique skills and the hunt needs his help to complete a mission. For example, a powerful monster is on the loose that only Percy can track down because of his connection to the sea. Another could be a love triangle between Percy, a huntress, and someone from Camp Half - Blood.
One plot idea could be Percy discovering he has the ability to bloodbend and struggling to control it. He might be afraid of the power and how it goes against his usual water - based abilities. Another could be Percy having to face an enemy who uses bloodbending in a malicious way, and he has to learn it quickly to defend himself and his friends.
One idea could be Percy joining a high - stakes tournament. He uses his unique skills and quick thinking to outwit his opponents. Another could be Percy playing in a team where he has to deal with a difficult teammate but manages to turn the situation around and lead the team to victory.
One idea could be a time - travel plot where Percy goes back in time and meets a younger, different Medusa before she was turned into a monster. Another could be a story where Medusa somehow gets a chance at redemption and Percy has to decide whether to trust her or not. Maybe a plot where they have to team up to defeat a greater evil that threatens both of them.
One idea could be Percy exploring his newfound godling powers and how they differ from his demigod abilities. He might accidentally cause some chaos in the mortal world while trying to master them.