Mabel's afraid of thunder but her brother's there to comfort her. Sibling love, not intended to be romantic in anyway. These two are so cute, I can just imagine something like this happening.

Astraphobia is the fear of thunder and lightning.

I also can't claim to own Gravity Falls. Darn.

Dipper woke up to the sound of violent shivering and fearful gasping. It wasn't an unfamiliar sound, but it did give him reason to worry. He looked out his window, and as if on cue lightning ripped through the sky and the threatening boom of thunder was heard soon after. A few years ago he'd've been in the same condition as the person across the room, but at some point, the fear of storms left him. He wished he could say the same for his sister.

He was about to say something, but she beat him to it. "D-d-dipper? A-are you awake? I-eep!" Her whisper was cut off by a quiet shriek caused by the raging thunder.

Dipper didn't say anything, he just sighed, and sat up, and glanced out the window at the pouring rain. He turned back to the girl and frowned, he hated to see her so scared. And so he began the routine they'd had ever since they were little, whenever the sky was taken over by relentless flashes of noise. He moved the covers of his bed, the rustle barely heard over the rain, and walked to the other side of the room. Lightning pierced the darkness as he searched for his sister's form and saw her, curled up with her pillow and facing the wall, her head buried in a sheet.

"Mabel, you're ok, the storm can't hurt you." Dipper said as he pulled back the covers and climbed into the bed with his sister. He grabbed her by the waist and pulled her into his arms. Most of the time, when her brother did this, she'd be paralyzed with fear, so he didn't expect her to say anything. He just pulled her covers over them and decided to wait out the storm.

Mabel suddenly turned over and buried her face in Dipper's shirt. He felt her tears on her chest and pulled her tighter. "Thanks, Dipper." She paused. "How did you do it?"

He looked down at his sister quizzically. "How did I do what?"

"How'd you get over it?" She pleaded. "I-AAAAH!" She pulled him closer and trembled as another clap of thunder sounded outside. "I c-c-can't let g-go of this, this fear th-that I have. I know it's stupid but I'm just so scared..."

Dipper waited until she was done to reply. "I don't really know. I guess I just found scarier things to worry about." She shivered again. "I think at one point I thought I couldn't ever help you unless I sucked it up and got over my own fear." Mabel shifted and loosened her death grip on him. She smiled, but it quickly dissapeared as the house shook again. "Don't worry, Mabel, you'll get over it someday. I'll be here until then."

"Dipper, there are adults that are scared of thunderstorms," She reminded him, "What makes you so sure I'll get over it?"

"You're already really brave Mabel. You saved me from a bunch of gnomes, and that psycho-I mean psychic Gideon. I'd be dead if it weren't for you." He smiled down at her.

"Completely different situation." She reminded him.

"Yep. What's a little electricity to being chased by Gnomezilla?" He smirked.

"You know that's not what I meant." The twin were silent before she screamed again as the thunder, louder this time, struck again. "That, Dipper, is what I meant."

"Well, Mabel, at least I didn't have to pry you out of a corner this time. You're doing better." Both twins smiled, because they knew he was right. They sat in silence, with the occasional shriek from Mabel, as the storm continued. Eventually Mabel fell asleep, and Dipper, finding her still having a vice-like grip, fell asleep on her bed too. The next morning, Dipper was the first to wake up, but it was still dark out and he'd still need a crowbar to get Mabel to release him.

After a few minutes, he heard her voice tentatively whisper from his chest. "Dipper?"

"Yeah, Mabel?"

"Thanks, you're the best brother ever."

"You're the greatest sister ever."

"You're just saying that."

"Nope."

They stayed in their embrace as they watched the sun rise, happy things were back to normal.

I love how there's so much sibling love in this show. Sibling love rivalry. And it's so cute!