One interesting P - Valley fanfiction could be about the backstories of the dancers before they came to The Pynk. It could explore their dreams and how they ended up in that line of work.
Think about the setting. You can expand on The Pynk, describe it in more detail, or create new locations in the same universe. Then, come up with a unique plot. It could be a love story between two minor characters, or a mystery involving the club's finances.