The sun was hanging slightly low in the sky by the time Stan Pines had started his spitting, growling engine, and with the gas still floating off and puncturing holes in the atmosphere, he lingered inside barking orders and expectations and reminders to his great niece and nephew. They swiftly nodded, sharply paying attention, and assured their uncle that he could take off for a day or so without the business completely going to hell.
"Dipper, you and your sister make sure the Shack is spotless when I get back, got it? And hey, raid the back room for a new attraction if you can. I don't care what it is, something's gotta work back there." He aimlessly scratched the back of his head, lacking the fez that normally adorned it. "Whatever brings in money."
"I'll see what I can find." Dipper responded dutifully.
"I'll be back tomorrow around this time." Stan added. "And, uh..."
He grumbled something under his breath, and turned to Mabel.
"I left 50 bucks on your bedside table in the attic. Order your brother a pizza or something, he needs meat on his bones."
"I will feed him so much pepperoni his head will spin," She grinned. "Thanks, Grunkle Stan!"
"Whatever, yeah, just don't ever expect me to spoil ya like that ever again," He turned away. "Can't have you kids dying on me, or anything..."
"Alright, alright, get outta here, old man!" Mabel playfully shoved him, smiling and waving all the way as he sped off in his car.
There was a brief moment of silence before the older of the twins sauntered off back up into the Shack, smiling and laughing and eager to enjoy working at her own pace with the other employees present. Her brother followed slowly, cracking his knuckles and figuring he might as well get a head start on finding something decent in the dusty old room locked in the depths of the building.
Dipper's sneakers creaked on the loose boards and cobwebs disintegrated around him like pixie dust. It was no wonder Stan so rarely ventured into this room—Dipper felt as though the floor beneath him would give out at any second, sending him plummeting into the dark yonder below the enigmatic shack. In this respect, everything in the room was untouched, but there wasn't exactly much potential to go upon. There was the generic poorly-stitched chimeras that tourists so easily ate up, machines and questionable illusions scattered everywhere, all of which had an abundance of smashed parts and long greyed from neglect. The perfectionist of a boy shook his head as he judged the potential attractions, none of this would do.
He was alerted abruptly to a dull humming coming from around the corner of one of the garbage heaps. It was the sound you hear when you enter a 24/7 gas station or are stuck in a building with cheap fluorescent lighting, and he'd found noises akin to it ominous ever since a certain fallout with some ghosts at a convenience store. Steadily, he crept toward the source, curious as to why precisely this one item had been left running while everything else was long abandoned and collecting dust.
The contraption was… surprisingly normal, when he finally feasted his eyes upon it. It was out of place with the LED sign crowning it, sure, but it was just a typical fast food soda machine. A weird kind of oasis amongst the wasteland, Dipper squinted at the writing on the front of it, casting a dull glow into the darkness of the room.
"'Soda Fountain of Youth'?" He pondered.
Grunkle Stan had a good amount of weird, unexplainable material hidden in the Shack. Sifting through what was legitimately supernatural and what was tourist-trapping garbage was the fun and often life-threatening sentence Dipper had taken upon himself when he first came to Gravity Falls. Upon further inspection of the machine he noticed that, where most soda machines have a decent selection of flavours appealing to the various patrons, this one only had two—he recognized them as Pitt Cola (sans pit, of course, but those things always annoyed him…) and Dr. Seasoning.
Cautiously, he took one of the paper cups sticking out of the bottom of the machine, carefully examining it for dust or bugs and finding none. Paranoid anyways, he blew on it cartridge-style a few times and skimmed the inside with his hands to make sure it was decently safe. Dipper took a breath and pushed the Pitt button.
The liquid that resulted was the same peach-coloured fizz he was always used to, but it had an otherworldly sparkle to it that took him by surprise. He poured it to the top, and sniffed it precariously to make sure it wasn't some age-old serum that was going to give him e. coli or kill him. Besides the glittery bubbles, it seemed just like any other soda.
This is probably a bad idea... was what ran through his head. But he was thirsty, and the machine was oddly preserved, and he figured this was in the job description. I guess if it kills me I'll die doing what I love, he reassured himself. Like that helped.
"Well…" He said out loud. "Bottoms up."
Dipper took a swig of the fruity ambrosia and was almost immediately hit with a fizzy wave that bubbled through his veins. So sudden he almost dropped the cup, it ended just as fast as it came. That was weird, he thought, but the only thing that had seemed to change was the fact that the soda fountain was now just barely towering over him. Was it another adventure in height-altering properties? No, it couldn't be… He turned the corner again, remembering a dusty old mirror just barely covered by a sheet somewhere back there.
Gazing into the browned glass reflection, he jumped and dropped what was left of the soda. His facial features had softened, transforming him with even more of an uncomfortable baby face. His clothes seemed to shrink with him, but the vest he constantly wore was puffy and gave him a look akin to an inflatable toy. His brown hair was so short that the starry silhouette on his forehead was bared for the world to see, and he reflexively lifted his hand up to cover it. Dipper almost screamed, but the thought of Soos or Mabel or god forbid Wendy finding him in this state silenced him enough. He remembered the writing on the LED sign, now; right. He groaned. Soda Fountain of Youth. That makes too much sense…
Combing his memory, he realized his age had to have been at least halved, but the fact that he was still capable of decent deductive reasoning and all his memories still in tact suggested that he had kept the mind of a 12 year old. Still uncomfortable but now mystified by this strange soda and it's age changing properties, he ran back to the soda machine and found a stray box to prop himself up on. Grabbing his spilled cup, he set it under the second flavour and stood on tip toes to press the button.
"If Pitt Cola makes me younger, then maybe Dr. Seasoning will make me…"
This time, he only took a sip, nervous about getting hit by another shock wherein his blood turned to pure carbonation. It was lesser, but as a result, he realized he hadn't grown much. The machine was still barely reachable, even on the box, and so he ran over to the mirror again to check.
"Well, I'm not 6 anymore, but…" He took another sip, and blinked his eyes open to another inch of hair, looking less like a balloon. "Is the amount you drink correlated to the amount you age or de-age?"
Testing the hypothesis, he braced for the impact and took a larger gulp, and opened his eyes to the horrendous haircut he had in the 6th grade. The cringing only lasted for a short moment before he realized that his guess was correct, so he took on last small sip and was reverted back to his 12 year old self.
"Glad that nightmare's over…" He sighed, and instantly perked back up. "I gotta tell Mabel!"
The boy sat his cup down and sped out of the dark room, greeted with an empty Shack, save for his sister, laying on the floor in the summer heat with her pig next to her, both of them on their backs and staring at the ceiling. He popped his head into her field of vision, an action that would probably startle a normal person.
"Where is everyone?"
She counted on her fingers. "Soos went to go fix the window upstairs, Stan's probably robbing a bank by now, aaand Wendy's probably slacking off on the roof and going over her breaktime!"
"Have we gotten a single customer?"
"Nahh," She rolled over. "It's pretty late in the day, anyways, and without Stan here there's no one to rip 'em off."
"Makes sense. Anyways, Mabel!" He waved his arms excitedly. "I found the coolest thing in the back room!"
"Is it a magical muzzle that'll revert Waddles' oinks to people sounds? Because we really need one of those."
"Even better!" Her brother grabbed her hand, excitedly scrambling to the back room as she trailed behind him.
She rolled her eyes, used to this by now, and sighed out a playful "I'll believe that when I see it."
"So you're telling me..." Mabel said, brown eyes peering up at the machine. "...that if you press these buttons and drink this stuff, we not only get to be whatever age we want, but free soda?"
"Isn't it awesome? You could seriously manipulate your age at will!" He journeyed off into an excitable tangent. "There's nothing in the book about this! It's the discovery of a century, if we had this we could parade around as grownups all day and no one would know the difference!"
"Free soda, Dipper!" She said in a voice so intense it almost seemed as if she was mocking him. "They have Dr. Seasoning, too! When's the last time you saw a brand that wasn't Pitt in Gravity Falls?"
She ran to the machine giggling, kicked the box out of the way, and excitedly poured a cup, all the while Dipper was muttering terms and conditions into her ears that she neglected to care for. She raised the plastic to her lips, chugging down the fizzy brown liquid and being thrown off her feet when the transformation hit her.
In front of Dipper stood his sister, towering over him and from the looks of it, somewhere around 20. The sweater and skirt she was wearing had grown with her and her hair had taken on a slightly reddish tint. When she smiled, her braces were gone, and a row of perfectly straight teeth replaced them. Immediately, she noticed the changes, picking her little brother up and smooshing his face against hers.
"This is so COOL!" She squealed. "I'm a grown-up! And I have money! I can buy all the juice I want! With a credit card! Grown-ups use credit cards, right?" She hugged him harder. "Let's get a credit card! Where do you buy credit cards?"
Dipper struggled free, falling back to the floor. "Mabel, we need to eat. Don't go too overboard, I know this is exciting, but..."
"Hey," She whispered. "How come you're still little?"
"I dunno, this is cool and all, and it'd be fun to be grown-up, but..." He kicked his feet. "What real benefits would it have? I'd just kinda be a pre-teen in an adult's body..."
"Dipper, how can you be so dense!" She kneeled down and grabbed his cheeks, staring him in the face. "Don't you get it? You don't have to be just an adult or just a kid!"
He blinked, not following.
"You could be a teenager, if you wanted!"
"BLARRR! YOU COULD PARADE AROUND AS A TEENAGER AND ASK A CERTAIN TEENAGE GIRL YOU LIKE ON A DATE, STUPID!"
All the colour drained from the younger boy's face, and he stared his sister down.
He didn't speak a word, but his expression said it all, so Mabel proceeded. "Think about it, Dipper! She'd never know it was you, you could actually get close to her and have the night of your life. Nothing could stop you!"
"You... you're right, Mabel... but... I can't stay like that forever. What about when I have to change back?"
She shook her head. "This is an opportunity you might never get again, Dipper! Don't overthink the future, just go for it." Leaving it at that, she handed him her half-drank cup, her muddy eyes a mirror image of his, even through all the years she had aged.
Dipper looked down into the rippling surface of the soda, nervously swallowing. His sister was right. It was weird to think about-him taking on an alter-ego and—jeez—asking Wendy out? How could he be sure she'd even say yes? But she had a point—there was no harm in trying. If he got rejected, he could always just revert back and they could blow their money on ice cream while Mabel comforted a sulking Dipper. Weighing out the pros and the cons, he gave up on thinking at the last second, and gulped down what was left of her cup.
The metamorphosis didn't hit him too bad this time as he had not only braced for it, but was conditioned to it by this point. Instead it felt soothing, like he was becoming... stronger? He knew that when he came out of it, his body likely wouldn't be too different—considering Mabel's. So he kept his expectations low, and chalked it up to the miracle soda rushing down his throat.
His sister's hushed, excitable gasps woke him from his stupor and she was gazing giddily at him, the two of them finally at eye level. Saying nothing, she dragged him over to the mirror, unable to stop smiling, and Dipper saw his older self for the first time.
"Woah..." He whispered.
In his reflection he saw himself, a total stranger. He was wearing his normal clothes, but his face had grown somewhat elongated into one with structure, all that remained of his chubby cheeks was a slight roundness under his eyes. His hair was curly and messy and fell just above his eyes, like he was used to. The greatest change of all, however, was the badge of honour now adorning his chin.
"I have a goatee!" He beamed, exchanging enamoured looks with his sister. "I have facial hair! Hair! That isn't on my head!"
"Dude, you don't even look like you! She'll have no idea! Your voice is deeper and everything!"
"This is so surreal! But..."
"I can't do it like this, I'm like, 20!" He crossed his arms. "That's like, majorly illegal. I need to be her age, maybe a year or two older..."
Without another word, he traversed back to the machine with his sister following behind, and poured a cup of Pitt, taking a few sips until he was decently teenaged, by his predictions. His goatee had been reduced to a patch of fuzz now, and he quietly stroked his chin while he mourned the lost friend.
"Someday..." The teen whispered.
Mabel nodded at him approvingly, and grabbed his hand, leading him cautiously out of the room. "One last thing," she said. "You're not convincing anyone with those clothes. You still look like you're twelve mentally."
"I kinda am..."
"Well, who cares! We need you to act like you're 16. We're raiding every closet this place has. C'mon, I'll go on ahead to make sure someone doesn't see you." She drank the last of his Pitt until she was little Mabel again, and quickly put her plan into action.
"This is going to be the makeover of a century," The girl whispered through a wicked grin as her and her brother left the catacomb of mystery.