Contains spoilers, if you haven't seen the entire show.
Several years after the events of the show.
Dipper and Mabel return to Gravity falls,both now 17, for a summer reunion with their friends and Gruncles. However the morning after they arrive a strange boy with golden hair appears on the doorstep of the mystery shack, with no memory of who he is or where he came from. The only thing he seems to remember is his name. Bill Cipher.
(Triggers for mentions of suicide, self harm, depression, anxiety, past trauma and past abuse.)
[Bill Cipher x Dipper Pines fanfiction]
Since the first summer Dipper and Mabel spent in Gravity Falls they've been going back every year. Now the twins are seventeen and still love the unknown future events of the summer. But this summer will be different.
Mabel is now seeing a boy and is too deep in her perfect romance to go back to Gravity Falls. Dipper tries to convince her, but she is too stubborn. He knows that this boy will probably break her heart like all the others, but he decides to let her stay to figure that out on her own.
Dipper ends up going alone and is spending the summer at the Mystery Shack. He works the cash register in the gift shop during the day and spends his nights alone. Little does he know that this will all change soon.
A certain demon by the name of Bill Cipher has liked Dipper since the very first summer. That attraction only grew over time. Dipper knows that Bill exists, but has never thought of him in a romantic way until a certain chain of events takes place. What changes Dipper's mind?
[SPOILERS!!!]