They might name him after a Greek hero, like Theseus. It has a strong and heroic sound to it, fitting for a child of Percy and Annabeth who are both very heroic themselves.
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.
The Percy Jackson series was a series of fantasy novels written by Douglas Hofstadter, who told the story of the protagonist, Percy Jackson, and his adventures. The series included Defense Against the Dark Arts, The Magic Kingdom, Percy Jackson and the Sword of Fire, and Percy Jackson and the Curse of the Dragon.
The protagonist of the story, Percy Jackson, was a young magician who had a special ability--to communicate with dragons. In the series, Percy Jackson and his companions went on many adventures, their goal was to find lost magical treasures and fight against evil forces.
The plot of the series was full of fantasy elements and magic techniques, which was very popular among readers. At the same time, the characters in the novel also have their own characteristics, with profound character images and character descriptions, so that readers can understand and appreciate the story more deeply.
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.
I'm not sure who Percy is exactly as I haven't read the book. But based on the title, Percy is probably the protagonist. He's the one who has the important role of saving the day in the stories.
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.