No, Percy Jackson is a hero in the original series. However, in fanfiction, different writers can have their own interpretations. But it's quite a stretch to make him the devil. Fanfiction sometimes just likes to play with extreme ideas to create shock value or new plotlines that deviate from the source material.
Maybe they want to explore the dark side of the Percy Jackson universe. By making him the devil, they can create a completely different kind of story, full of chaos and moral ambiguity.
The devil could be a new, mysterious character created specifically for the fanfiction. It might be an ancient evil entity that has been lurking in the shadows of the Naruto world for ages.
I'm not sure as the statement doesn't provide much context. Percy could be a character unique to that particular fanfiction. It might be a character created by the fanfiction author with certain special traits since they are described as 'the oldest being' in this work.
Percy in 'percy controls poison fanfiction' could be a character that the fanfiction author has designed with unique abilities related to controlling poison. Maybe it's someone inspired by a real - life figure, a historical character perhaps, but more likely it's a fictional creation within the realm of the fanfiction. It could also be that Percy is a character borrowed from a popular book, movie, or game series, and the fanfiction writer has given them this new role of controlling poison for the purposes of their story.
There's also 'Female Percy: A New Heroine'. Here, Female Percy brings a fresh perspective to the story. Her fighting style is different, more fluid perhaps. And her relationships with the gods are also unique. Instead of the typical male bravado, she uses her wits and charm to get through tough situations.
A popular one is 'Percy and Annabeth's New Quest'. In this fanfiction, the author takes the duo on a quest that wasn't in the original books. They have to solve ancient riddles and battle new mythical creatures. It stays true to the characters' personalities, making it a great read.
Percy could be an original character created by the fanfiction author for this specific story. Or he might be a character borrowed from another work, like Percy Jackson perhaps, and given this new 'controls all elements' ability in the fanfiction world.
You can start by looking on fanfiction.net. It has a large collection of 'Percy Jackson' fanfictions, including many that focus on Percy and Piper. Just use the search bar and type in relevant keywords like 'Percy and Piper' and you'll get a bunch of results.
One great 'Percy Jackson, Percy and Piper' fanfiction is 'The Adventures of Percy and Piper'. It really captures the essence of their characters. The author does an amazing job of creating new quests for them while still staying true to their personalities from the original series.