One idea could be that Percy Jackson is discovered by SHIELD. Maybe they initially mistake him for a mutant or some new kind of enhanced being. They try to study him, but Percy is having none of it. He uses his powers to escape their facility and then has to outwit SHIELD agents while also dealing with some mythological threat that has emerged in the modern world. This could lead to some interesting interactions as Percy tries to keep his identity as a demigod a secret from SHIELD.
It could be a die - hard Percy Jackson fan who has a lot of creative ideas and wants to explore new aspects of the story. Maybe someone who has been reading the books since they were young and has always dreamed of adding their own twist.
Perhaps the fanfiction's plot involves Percy secretly being part of a prophecy that the gods are trying to keep hidden from the demigods. This could lead to him having to make some tough choices between his loyalty to his friends and his new - found secret destiny.
Well, first, the world - building would be crucial. The two universes have very different rules. In the Percy Jackson world, there are gods and monsters from Greek mythology. SHIELD, on the other hand, is all about modern - day espionage and advanced technology. A good way to make it work would be to have a sort of 'portal' or 'rift' that connects the two worlds. Maybe some ancient artifact that SHIELD discovers opens up this rift. Percy could be drawn into the SHIELD world through this, or vice versa. Agents of SHIELD could be sent to investigate the strange happenings in Percy's world.
The most exciting crossovers would likely involve Percy's unique abilities in the context of Shield and Avengers' missions. His ability to heal himself in water could be a huge asset during a dangerous mission. He could also use his underwater combat skills to take on enemies in a way that the Avengers or Shield agents aren't used to. Maybe he could even use his powers to help the Hulk calm down by creating a large body of water for him to relax in, which would be a really unique and interesting scenario in a fanfiction.
A powerful new demigod who is jealous of Percy's secret power could be the main antagonist. This demigod might think that Percy doesn't deserve such a power and tries to steal it for himself. He could be a son or daughter of a minor god who feels overlooked and wants to use Percy's power to gain recognition.
A possible plot for a 'Percy Jackson Secret Power' fanfiction could involve Percy having a secret power of teleportation. But this power is not fully under his control at first. He might accidentally teleport to strange and dangerous places. One time he could end up in the middle of a Titan's lair. As he tries to master this power, he discovers that it has a connection to an ancient prophecy. His friends, like Annabeth, help him figure out how to control it and use it for the greater good.
Well, in some fanfictions, Percy might control ice through a new power bestowed upon him by some mysterious god or entity. Maybe he discovers he has the ability during a quest when he's in a really cold and magical place.
It could be Annabeth's sister (if she had one). A new character who has all the intelligence of Annabeth but a different personality. Percy might be drawn to her because she challenges him in a different way. Maybe she's more into art and architecture rather than just battle strategies like Annabeth, and Percy finds this new perspective fascinating.