The moon shone brightly through the window as Mabel glanced across the attic towards a comfortably dozing Dipper. How could he do it? Sleep? Even in her tank top and pajama shorts, Mabel couldn't get comfortable. They only had twenty-three days left together - not like she'd been keeping track or anything - and then WHAM. Different colleges, across the state. At least they'd both still be in Oregon, and could come back to the Mystery Shack for the summer, right?

That wasn't quite enough for Mabel. Thinking about how her brother would change in college - his clothes, his style, his - everything! He wouldn't be HER Dipper anymore, the one she knew everything about. And what if he brought a girlfriend back over the summer? How long would she be there? Would the Stans let them share a room together? How much would Mabel have to interact with this hypothetical girl with her oversized bracelets and terrible makeup and GOD KEEP IT DOWN ALREADY WITH THE DANCE POP? Ugh. Too much to think about right now. Too uncomfortable.

She looked over at Dipper again. So many memories. They were always together! The Mystery Twins! Dipper's dumb, nervous detective schpiel when investigating paranormal whatevering? Mabel was more than happy to go along for the ride, seeing Dipper get so excited. The thought of Dipper's Patented Dumb Doofy Grin For His Dumb Stupid Face (TM) made her smile. And him lying across the room in his bed always made her feel safe. That's how they justified still sharing a room with everyone- once all the news crews found out about Gravity Falls, there was no shortage of weirdos wandering around hoping to get a glimpse of some gnome or dinosaur. And some of them were, well, weird. Dipper always had so much patience with them, answering their questions about the town, and explaining the new Mystery Shack outlets the Grunkles had set up at various "hot-spots" around the county. But if any of them ever broke into the Shack? Dipper would kick their butts, no questions.

Mabel realized she was still staring. No, worse. She was staring at Dipper. While he was sleeping. Chest slowly moving up and down, stable breathing, KO'd, down for the count asleep. So why couldn't she do it? She sighed. Maybe... she'd go pick his brain? At least snuggle up and steal some of his heat. It was freezing up in the attic, right? And Dipper always slept in his boxers because he was so warm. Slowly Mabel rose, grabbing her pillow and tiptoeing across the creaky oak boards. Why was her heart beating so quickly?

Dipper moved slightly as she poked him. "Mrmmmmmmmm."

"Dips, scooch over. Mabel's coming in." Mabel climbed into the bed, as Dipper groggily shifted around. As she climbed under the sheets, Mabel could feel his warmth from where he had just been lying. They had shared a bed occasionally when they were younger, but not since puberty had muddled things up.

"What up, Mabes?" Dipper grumbled, still half asleep. Urrrrgh. What WAS up?

"I can't sleep, so I figured that I'd come steal whatever magic jenk you've got working for you."

"No magic here. Just good ol' fashioned American ingenuity." Dipper yawned, and started to turn over to go back to sleep.

"H-hey, wait!" Mabel started, as Dipper turned back to look at her. "We... we haven't talked about college yet. What's going to happen with... with us? I mean, you have to have thought about this, right? 23 days, and we're going to be on our own?"

Uh, wow. Mabel sounded much more - frantic? - then she had anticipated. Thankfully, Dipper didn't miss a beat.

"Mabes, don't freak out, okay? We're the Mystery Twins. Nothing's gonna keep us apart, you know that. Listen. You're my favorite person in the whole world, and I love you more than anyone. Something as lame as different colleges isn't going to keep us away from each other."

He reached out his hand, gently stroking her cheek. Wow, their faces were really close huh? Annnnd, yup. Hers was definitely blushing, judging by how hot her cheeks were. And there was Doofy Grin (TM) making an appearance, right on schedule.

"Thanks, Dipper. I... I love you. I love you too. But it's weird? I really, just... it's just that I don't want you to go. It's not fair, and we can't do anything about it, but I wish we could stay... together? I really don't want to have to live... without you? And look at the Stans, they're twins! And it's all just working out for them now, after all their problems. What if that's us, Dipper? What if we drift apart? I just... it's just, I love you so much, I really don't think I can handle that!"

Tears were streaming down her face, and Dipper's grin had been replaced with a look of concern.

"Mabel, I didn't know you were this worried," Dipper whispered softly. Sadness tinged the edges of his face now - his stupid, adorable face - "I mean, what kind of terrible brother am I here anyway? Of course you'd be upset! Ugh." His face wrinkled up. "I mean, I've just been forcing myself not to think about it, that it must be better for us to go off on our own - but that's just it. I don't want to do that. Obviously we can't be together forever, but... like, didn't you always assume we would? Dipper and Mabel! Mabel and Dipper! You're basically the other half of me, and we - us - can do so much when we work together. And now it's here, it's time, and all I can do is just pretend like nothing's changing." He stopped, running his hand down Mabel's cheek once again. "But... things have to change. Right? That's how we move on, how we grow." He forced a smile.

Freaking Dipper's stupid, handsome face making stupid freaking valid points. Gotta shut him up. She kissed him. Not a peck on the cheek, not a gentle tap on the lips. No, this was the full on, mouth-on-mouth "holy shit we should not be doing this or anything remotely like this" kiss that she knew she wanted to give him the second she crawled into his bed. Wait, were they still kissing? She pulled back. Dipper blinked back at her. Oh shit. Oh shiiiiit. She had just swapped saliva with literally her closest living relative, oh no, oh jeez, hit the panic button, everybody pack it up, Autobots roll out, burn it down, better luck next time - and now he was kissing her.

No hesitation this time. No pretense, no history, no nothing except two teens in love, swapping spit alone in an old attic. Dipper was much better at kissing than she had expected - back when they used to practice together, Dipper's approach had always been "MAXIMUM TONGUE OVERDRIVE" - but now, he was much more gentle. Nipping at her lip, kissing her neck, stroking her hair. Hnnngh.

But she knew Dipper. This is as far as he'd go on his own. In a few minutes, they'd stop, and have to talk and talk and talk about everything that just happened. Not good enough. Just... not good enough. Mabel wanted, needed, and craved more. She slipped her hand under the covers, rustling around and brushing against - what? No way. Slowly, she rubbed her hand along the length of his boxers to double check. Hypothesis confirmed, visual confirmation required. Roughly, Mabel yanked off the rest of the covers, letting them fall on the cold attic floor.

"H-Hey Mabel," Dipper stuttered, "Wait, are you sure this is, uh, what you want? Er, I mean, uh, shouldn't we talk first, figure out if this is really the right gameplan here?" Slowly, she unbuttoned his boxers, drawing out his extremely hard and extremely large cock. Of course they had seen each other naked by accident while living together for so long, but this was her first real up-close experience with what could only be categorized as his 'monster dong.'

"Uh, sorry what, I wasn't listening?" Mabel answered, gently moving her hand up and down his sizable shaft, watching him squirm slightly and feeling his heat in her palm.

"MMmm nnnevermind, fuck it," Dipper managed to mumble, breathing becoming heavier as Mabel continued her efforts. After a minute, she stripped off her tank top - not like it had been hiding much anyway - letting her ample breasts flop out. "Oh fuck that's hot," Dipper grunted. His penis agreed, judging by the subtle change in density - christ, did it get bigger?

"Oh yeah? You like 'em?" Mabel grinned devilishly, waving her chest back and forth in his face. Dipper reached out measuredly, cupping a breast gently in each of his hands in response. Slowly, his thumbs brushed against her nipples. A jolt of electricity shot down her spine, and she couldn't help letting out a small moan. Dipper's soft hands continued to squeeze, grope, feel and fondle as Mabel felt her temperature shoot up another ten degrees.

Enough waiting around. Mabel pushed Dipper back down onto the bed, ripping off his boxers entirely. Her shorts came off in a simliar manner. She pulled herself against Dipper, their naked flesh pressing together. His heart pounded through his chest. Her own matched the beat. They were truly in sync, twins, in a way they had never been before. Neither moved for a moment. This was crazy, right? But no turning back now. She wanted it too badly, and judging by Dipper's continued 'enthusiasm,' he did too. They were in this together, just the two of them.

Mabel broke the unspoken truce, turning to dig around in Dipper's nightstand - and score! A condom. Dipper's eyes widened as he saw her unwrap the square and unroll the latex right onto him.

"There's no coming back from this, is there?" Dipper asked, quietly.

Wordlessly Mabel grabbed his penis, guiding it into her now-sopping enterance. Both of them gasped as Dipper began to slide in, slowly managing to fit all the way in to his base. Mabel was shocked it managed to all fit, although that thought soon went out the window along with most of her other cognitive reasoning as Dipper began thrusting. She came almost immediately, but it didn't stop there. Dipper kept going, picking up the pace to find a steady rhythm. They kissed again, tongues bashfully mashing as inhibitions slipped away. Mabel found herself unable to hold a thought as she looked up at her brother above her, his eyes blank and face distorted with waves of bliss. So handsome, so strong, and so... gifted. She let herself dissolve into the waves of pleasure.

-x-

The sun began to shine softly through the window as Mabel glanced over to her naked brother still next to her in his bed, comfortably dozing.

How could he do it? Sleep? They only had twenty-two days left with each other.