Another possibility is that Percy is recruited by a secret organization that has discovered his demigod powers. They see his potential as a secret agent because of his combat skills, quick thinking, and ability to adapt in dangerous situations. In this fanfiction, he might have to work with other agents who are initially skeptical of his 'weird' powers but soon come to respect and rely on him.
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.
One possible plot could be that Percy and Annabeth are secretly recruited by the gods to be agents in the human world. They have to use their demigod powers and skills to stop a powerful ancient evil that is using modern technology to cause chaos. For example, a Titan might be using the internet to spread misinformation and create unrest among mortals. Percy could use his water - controlling powers to deal with any threats related to water systems, like floods created to disrupt cities. Annabeth, with her strategic mind, would be planning their every move and deciphering the Titan's plans hidden in ancient texts that have been digitized.
One common plotline is Percy using his demigod powers in a secret agent - like mission. For example, he might use his ability to control water to infiltrate a secure location near a body of water. Another is Percy teaming up with other demigods as a secret agent squad to take on a new threat to the demigod world that has a more modern, espionage - like feel.
There's also 'Secret Agent Percy'. It was interesting how Percy was paired with a mortal agent who didn't believe in the supernatural at first. As they worked together on the mission to stop a group of rogue demigods from starting a war, the mortal agent gradually came to accept Percy's powers. It had a great mix of action, humor, and character development.
The main enemies could be the Titans who are still bitter about their defeat and want to regain power. They could be using secret agents of their own, disguised as mortals or demigods, to carry out their plans. Another enemy could be some rogue demigods who have been corrupted by power or greed and are now working against the good of the demigod community.
Well, a plot could be where the government discovers the existence of demigods like Percy and tries to control them. Percy then has to decide whether to cooperate or fight against this new form of 'government'. He could also be part of a team of demigod - government agent hybrids, where they have to deal with threats from both the mythological world and human threats that the government can't handle on its own.
Yes, there could be. Writers often like to cross over different fictional universes. In such a fanfiction, Percy Jackson's demigod skills would be interesting to incorporate into the world of Shield agents. Maybe his water - controlling abilities could be used in some sort of covert operation, like creating distractions or even rescuing agents in a flooded area.
Fanfiction.net is also a great place to look for such fanfictions. A lot of fans post their creative works there. However, the tagging system might not be as detailed as AO3, but with a bit of searching, you can still find some interesting 'Secret Agent Percy Jackson' stories.
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.
Another possibility is that Percy is sent to Hogwarts undercover as a Hufflepuff student to investigate some strange magical activity that might be related to the Titans or other Greek monsters. He has to keep his identity as a demigod a secret while trying to fit in with the Hufflepuff house. He could learn a lot from the Hufflepuff way of life, like their patience and kindness, and in turn, he could teach them some things about courage in the face of danger that's different from what they're used to in the wizarding world.