She's Mine (Bill Cypher Fanfic(Human for the most part))

Riley Fleur is forced to move to Gravity Falls Oregon with her grandparents even though she wants to stay in Portland. She has plenty of friends but ghosted them when her parents decided she would stay with her grandparents instead of staying with them for the summer. She doesn't know how long she will stay after the summer, her parents told her it all depended on what she wanted.

Riley knew she wanted to stay but they didn't give her a chance to. She meets the Pines and already knows Pacifica, the house her grandparents own is right next door and almost as big. But she would rather keep to herself in the summer one necklace proves that will be a lot harder than she thought. While befriending the Pines, they tell her all about Weirdmageddon, which happened all because of a certain demon.

Follow Riley Fleur through her adventures with the Pines along with a certain demon who thinks he already has a claim on the girl.
(This is obviously set after Weirdmageddon but not a lot after, it's like a few years after. I own the story and any OC that may come along, the rest is owned by disney.)