Let's take a crack at Gravity Falls on Fanfiction and see where it leads.
Things to know about this AU before diving in: This is set in NWHS but before anyone can do anything about the portal, while Mabel is suspended in the air, she gets sucked into the portal and it collapses afterwards. She meets Ford on the other side and lives with him for ten years. She earns her scars and heartbreak and ends up getting a more secluded personality instead of being bright and fuzy. She returns ten years afterwards at the age of 22 and reunites with her twin brother who had never stopped trying to save her.
This is not in any way going to deal with romance. I want to explore the effect the portal and being left alone would have on the twins and how they attempt to patch things up. So enjoy! Everything revealed in due time.
It hadn't exactly ended as it did in fairytales and cliché chick flicks. Mabel already knew what to expect from people and the world around her. She expected the worst so she wouldn't be disappointed when things went sour.
She had accepted that she would never see Dipper again. She accepted that the last time she would see him was when he was scared, frightened and crying. It had been over ten years since she had last seen him and she was starting to forget what he looked like. Maybe she had kept her hair short because she knew she would look like Dipper.
She tied a piece of rag in the short curly mess, quickly realizing that the short haircut made it easier to escape from people. Long hair was just another weakness when she had to make quick escapes.
She accepted that she wouldn't find Dipper ever again and learned to survive beside her Great Uncle Ford (Boy that was a surprise that had her in hysterics when she was twelve). He kept her close and away from most of the fighting before she proved her worth. She had seen horrors no kid should ever see and her innocence was stripped from her. But she didn't care because she had to keep Ford safe. She had to keep herself safe because, damn it, she still hoped.
She still dreamed about seeing Dipper again. He alternated ages in her dreams. He was either twelve with a bright smile or an awkward teenager. She knew she based it on herself and she didn't care. Dipper made her days a little brighter and made her heart waver when she felt like she was losing herself in the darkness of the fight.
She dreamed of going home, about being in Dipper's arms, being with Waddles and attending high school. She thought about making Mabel juice, patching things up with her Grunkle Stan. It always ended happily without any cares in the world.
She didn't factor in the fact it had been ten years since she last saw her brother. She didn't factor in the way she felt wrong when she thought about all the things she had done.
She didn't think about Dipper's feelings.
It was ten years before she was finally returned home.
Dipper was different. He wasn't twelve anymore and his body had filled out with lean muscle. His hair was pushed back, looking windswept and revealing his Big Dipper birthmark. His eyes were wide, staring at her as she finally disposed of the extra weight on her body. She didn't care, she thought. She flung her arms around him, making him squeak before he stepped back, squeezing her and twirling her. They stayed together for a very long time, feeling the warmth of their skin and the beat of hearts that sang 'twins.'
Dipper trembled beneath her arms and breathed her in, whispering the words she had always dreamed about. 'I missed you, Mabs.'
She quickly realized she really didn't know nothing about her twin brother. The night that they had returned home she had been woken up by soft voices in the hall outside of the room she was in. Apparently her old room needed to be cleaned (They didn't think the portal would actually work).
"You got a call from Blubs." She heard her Grunkle Stan say as she laid in bed.
"What was it this time?" Dipper mumbled, sounding sleepy. He confirmed her thoughts as he yawned, the soft snapping of his jaw could be heard in the silence of the house.
"He said the Fairies are stealing food from his garden. He tried to shoo them but they retaliated and scratched him."
Dipper hummed, probably on his way to the restroom. "I'm on it. Probably a shortage of food in the woods. Stupid Gnomes. I won't be back till late."
Stan grunted. "Let me patch you up."
"What? I'm not-"
"Kid, how long have I been watching your ass? Ten years. I know an injury when I see one. Come on."
She stayed silent, heart thudding in her chest painfully before they were muffled by the door to the restroom.
Dipper didn't come home till later, dirty and agitated while scratching at the bandaged forearm. He smiled at her, grabbed some food and headed back out with a 'be back in the morning!'
She quickly realized Dipper was never home anyways. She woke up at nights to realize he was gone and Grunkle Stan didn't bat an eyelash. She knew the forest was dangerous, probably not as dangerous as the portal but it was bad enough. She was worried. She just got her brother back; she was not going to let some asshat think they could mess with him.
One night she decided enough was enough. She got suited up, passing a quick hand sign with Ford she had mastered over the years before leaving the shack. She was dressed in a sleeveless turtle neck. Her baggy jeans fit her form snuggly and her assault rifle was tight across her chest.
She had felt just a bit of an inkling of her younger self when she saw the boxes of her colorful and bright sweaters (She hadn't asked about the other boxes of stuff from her home in Piedmont. She was scared about what that would mean). For now she wanted to hide herself as much as she could. Scars were hidden along her torso and legs. Her arms weren't any better but she could put up with them.
She followed after him carefully, years of experience engrained into her mind before she climbed a tree to look into the area Dipper had stopped at. It was pretty dark but he seemed to navigate with ease. He reached towards one of the trees, leaning in and speaking softly.
The forest lit up instantly. She blinked in surprise as tiny glowing balls began to hover around him. Her brother smiled brightly at them, holding out his hands for the balls to land on.
He was meeting up with Fairies. She had learned a bit about Gravity Falls after years of living with Ford. They calmed her down after panic attacks. Gravity Falls meant Dipper and now, as she watched him chat with the Fairies and play with them she felt like she was breeching his privacy.
She knew she couldn't leave till he did since she didn't want to get caught. She spent a few hours up there, her legs cramping until she gave in and shifted. She alerted the Fairies who hissed at her, making her lose her balance and fall right out of the tree.
"Mabel?" Dipper asked, batting his hands and holding one out for her to take. He seemed confused until he took in her attire and the guilty and embarrassed look on her face. "Were you following me?"
She stuttered, not sure how to phrase what exactly what she was doing before she took his hand and hefted herself up. She dusted herself off, flustered because she was coming up empty. "Would you believe I couldn't sleep and went for a walk?"
"Uh, yeah. But because you look like you stole my spaghetti I'm not buying it."
She grinned, eyes nervous. "Damn, worth a shot, right?"
"Mabel, seriously." He said, eyes holding a bit of anger. It was one of the only emotions she had seen him wear since she came home.
"I was worried." She admitted, holding her hands out in front of her in a nervous tick. "The woods aren't safe. I don't know what's in here and you're always going out." She bit her tongue at what she really wanted to say. She was scared to admit she was scared he would get hurt. It felt like it wasn't her place to say it.
"Mabel, I don't need you to worry about me." He said, irritated as a few Fairies giggled, sitting on his shoulders as he crossed his arms over his chest. Some pulled at Mabel's hair, making her glare in irritation at them. "I'm sorry if I haven't been around but I've been busy."
She made a motion at the Fairies to leave her alone, "I don't even know what you do, Dipper."
"I thought Grunkle Stan told you already." His eyebrows knit in confusion and a bit of hot anger bubbled in her chest. She knew she had to accept the worst but she was home, after years and years of torment. She wanted everything to end like in a movie!
"I want to hear it from you. My twin brother, okay?" She snapped, startling the Fairies as Dipper gazed in surprise. She played with her bracelet, calming down the rage in her heart. "It's weird, okay? I didn't expect everything to be hunky dory but I thought that-that at least you would be good with me." She gestured between them, feeling hot tears behind her eyes. "I thought that we would still have the cool twin closeness things but we don't and it scares me!"
There was silence between them and she felt like running again. She raised her hands to mess with her mess of short hair and pressed the thoughts about thinking she looked like Dipper out of her mind.
Dipper gave a sigh, raising a hand to press it against the back of his neck. "Fuck, Mabel I know but…" He broke off, looking out at the Fairies who hung off of his every word. "Alright, shows over. Get, I'll be over tomorrow to check on Granny Oak." The Fairies giggled, a few kissing his cheek before disappearing into their homes.
He grabbed her by the elbow and got her to walk onto the trail again. "It's been ten years. Things change."
'I don't want things to change!' She thought desperately. She ran her fingers through her hair, annoyed she couldn't chew on it anymore.
"People change." He added softly.
Her heart froze and she knew he heard her sharp intake of breath. He was right. She felt like he could suddenly see all of her flaws, all of her scars and she fidgeted, crossing her arms over her chest as a flush of shame washed over her. Think up, Mabel! She told herself, praying not to fall back into a pit of awful and icky feelings. She wanted to snuggle up with Ford again and it pained her to think how much she relied on the man.
"We aren't twelve anymore. We have different lives." He was speaking again, not noticing her sudden defensive behavior. "It doesn't mean we can't be close it just means that things will be different."
He stopped as they neared the shack, rubbing at his face. "Listen, I'm bad at this but we can make this work." He looked at her, the moon illuminating his face. It was still Dipper, even if he felt like a stranger. "You're still my sister. I promise I'll make more of an effort."
She gave a nod of understanding, not caring as he pulled her in for a hug.
She laid in bed for a long time, staring at the old rotted ceiling. It hadn't been an awkward sibling hug. She tucked herself into the blankets, pressing her face into the pillow and crying.
Somehow she hadn't returned to Dipper after all. She lost him long ago when she fell through the portal.