Well, you could write a fanfiction where the different pantheons are in a sort of competition. Percy, being from the Greek pantheon, has to represent his side. He teams up with some unexpected allies from other pantheons, like a Valkyrie from the Norse pantheon. They have to complete a series of challenges set by the gods of all the pantheons involved. It would be full of action, with Percy using his water powers in new and creative ways against opponents from different mythologies.
One idea could be a crossover where Percy meets characters from the Norse pantheon. He could go on an adventure with Thor and Loki, and they have to face a common enemy that threatens both their worlds. Another idea is to have Percy enter the Egyptian pantheon's realm and learn their magic and ways, maybe even form an alliance with Anubis.
You can make it unique by focusing on the relationships between the different pantheons. For instance, show how the gods from the Greek and the Aztec pantheons view concepts like honor and sacrifice differently. Percy could be caught in the middle of these cultural differences and have to find a way to reconcile them.
One idea could be a fanfiction where Percy and his friends go on a new quest in a modern, urban setting. Instead of the usual mythological locations, they have to deal with monsters hiding in big cities. Another idea is a story that focuses on the relationships between the characters in a more in - depth way, like exploring the friendship between Percy and Grover during their off - quest times. And a third idea could be a time - travel fanfiction, where Percy gets sent back to the time of the ancient Greek heroes and has to interact with them while still holding onto his modern values.
One idea could be to explore Percy's life after he has fully mastered his powers. Maybe he goes on a quest to find a long - lost relative who also has demigod powers. Another could be a story where Percy and his friends have to deal with a new type of monster that is immune to their usual weapons and they have to find a creative way to defeat it.
One plot idea could be Percy having to team up with Hera to rescue a group of demigods who have been captured by an ancient monster. Hera, despite her usual aloofness, realizes she needs Percy's unique skills.
One idea could be a crossover with the Harry Potter universe. Percy could visit Hogwarts and have to deal with both magical and mythological threats. Maybe he'd team up with Harry to defeat a common enemy that combines dark magic and ancient Greek monsters.
Well, you could write a fanfiction where Percy loses his memory and has to rediscover his powers and his place among the demigods. Or perhaps a story about how the minor gods in the Percy Jackson universe form their own alliance because they feel overlooked by the Olympians. You could also create a fanfic that focuses on Annabeth's journey if she was separated from Percy and had to fend for herself in a dangerous situation.
Another interesting concept is a story where Percy Jackson is somehow transported to the Marvel universe. He could use his water - controlling powers in unique ways there. Maybe he'd join forces with Namor, the Sub - Mariner, and they'd have an underwater adventure together, facing off against some underwater threat that only their combined powers could handle.
Well, one interesting idea could be Percy having new powers or abilities. Maybe he's reborn with the power to control not just water, but also other elements like fire or air. Another could be his relationships being different. For example, his friendship with Grover might start off on a more competitive note instead of being friendly from the start. And also, the whole concept of him being reborn might mean he has a different view of the gods, perhaps more skeptical or more understanding depending on his new experiences.
One idea could be exploring Percy's life if he had a different godly parent. For example, if he was a son of Hades, how would his powers and his relationship with the other demigods change? Another idea is to write about a time - travel adventure for Percy and his friends, where they go back to the era of the first Olympians.
One idea could be to create a fanfiction where Percy has to face a new type of monster that is a combination of different mythological creatures. For example, a centaur with the wings of a griffin and the head of a Medusa. Another idea is to write about Percy's adventures in a modern city that has been magically hidden from the mortal world, full of demigods and mythical beings living in secrecy. Or you could write a fanfiction about Percy training a new group of demigods, passing on his skills and knowledge.