Well, Jaune in RWBY fanfiction can vary a lot. Sometimes he's the underdog who overcomes huge challenges, and other times he might have unique powers or a special backstory.
It could be because Jaune is a relatable character. He starts off as a bit of an underdog in RWBY. So, fans like to write stories where the other characters notice his potential and become obsessed with him as he grows.
I'm not sure of a specific 'jaune is secretly a faunus fanfiction' to recommend. You could try searching on fanfiction platforms like Archive of Our Own or FanFiction.net.
One idea could be that Ruby and Jaune are partnered for a special mission outside of Beacon. Ruby's speed and combat skills combined with Jaune's strategic thinking could make them a great team. For example, they might be sent to investigate a mysterious Grimm activity in a far - off village. Ruby can quickly scout the area with her speed, while Jaune plans their approach based on the information she gathers.
One possible secret could be about his family heritage. Maybe in the fanfiction, Jaune has a hidden connection to a powerful family in the RWBY universe that he's kept under wraps for some reason, like to avoid unwanted attention or because of some family feud.
His character could become more self - assured. Jedi are known for their confidence in their abilities, and Jaune might gain that as he masters Jedi - like powers.
One possible plotline could be that Jaune has been hiding his Faunus identity to avoid discrimination. As the story progresses, his secret might be revealed during a crucial event, like a battle where his Faunus abilities give him an edge.
Ruby would most likely be involved. She's the leader of Team RWBY and has a strong sense of justice. She would be determined to find Jaune no matter what. Weiss could also be involved as she has the resources and skills to help in the search. Her family's influence and her own combat abilities would be useful.
Yang would probably have a very vocal reaction. She's not one to hold back her thoughts. She might laugh it off at first, thinking it's just a wild and crazy idea. But if the fanfiction starts to get into some deep and dark themes related to Jaune being Satan, she could become more serious. For instance, if it shows Jaune causing harm to their friends in the story, Yang would be angry and protective.