You are the sister of Wendy who just moved back to Gravity Falls after living with your mom for 17 years and only seeing your sister for holidays. You walk into the mystery shack where Dipper, Mabel, Waddles, Grunkle Stan, Zeus and Wendy were working in the gift shop

(For the record this takes place a few years after the fight with Bill cipher, so Both you and dipper are the same age)