“Carry the one… this battery should be able to take it, right? That should work as long as I-”
“Sis!”
 
Charlie heard the muffled voice of her younger sister from the other side of the door to her room.
“Siiis! Are you there?!”
Smiling, Charlie rolled her eyes as she stared at the door.
Her younger sister, Maddie, always showed a lot of interest in whatever she was working on. Being young and excitable, she loved to see all the weird cool chemical reactions, crystals, and other fun stuff Charlie could do.
“Yes, Maddie, I’m here” She spoke while giggling. “Where else would I be?”
“Well, mom and dad have said that they’re gonna be leaving soon!” Maddie continued to speak through the door, being just a bit too loud.
“Huh? Where are they going?”
“Oh, they told me to tell you that they were going to be gone for the weekend!”
“Wh- and when did they tell you to tell me that?”
“Like… a few days ago?”
Charlie laughed. Sighing, she walked to her door and opened it.
“Would you prefer to talk like this instead of yelling through the door?”
 
The open door gave the sisters a better view of one another. Charlie was average height for her age at 5’4, with golden skin, hazel eyes and straight reddish brown hair, and wore a brown tank top, grey sweatpants and white socks. Maddie was shorter at 4’1, with pale skin and blue eyes, it’d be hard to tell that they were sisters if it wasn’t for their similar facial complexion. She wore an oversized pink sweater, long enough that it also covered her legs nearly up to her knees, and she was barefoot.
 
 
As the door opened, Maddie’s eyes immediately darted away from her sister and towards the back of the room.
“Woah, what’s that?!” Her attention was taken to a chemistry set that had been meticulously laid out over her older sister’s large desk: Flasks, droppers, condensers and even a fancy vacuum chamber, all seemed to have been recently used. But before she could sprint towards it, Charlie grabbed the hood of her sweater, keeping her in place.
“Woah, slow down! Mom and dad are leaving soon, right?”
“Y-yep!”
“If we wait ‘till they’re gone, I can show you what that is!”
“Ooh!” Her eyes seemed to glow. Charlie was usually very secretive about her work, usually due to the potential for Maddie to hurt herself while using it, so the idea of being able to see one of her inventions up close got her excited very quickly.
“Do we have to wait till they go?! Can’t you give me a hint?!”
Charlie looked at her sister’s eyes. She couldn’t say no to that excitement.
“Well… let’s say that it’s capable of creating toys!”
Maddie opened her mouth in surprise, gasping audibly.
“Does that m- mphphpm?”
Seeing a barrage of questions coming, Charlie put her palm over Maddie’s lips, sealing her mouth shut.
“I’ll tell you when we’re alone, alright?”
“...” Mouth still covered, Maddie nodded up and down.
“Great! Now, let me finish this up and come back when our parents are gone, huh?”
Charlie teasingly pushed Maddie towards the door. She ran out with a “M’kay!” as Charlie closed her door, sighing.
“Whew… this girl.” She walked to her chemistry supplies, checking how her solution was doing.
It had been sitting under a flame for a few minutes now, and it was nicely changing from a brownish red to a more transparent pink color. The last of the chemicals were dissolving.
When it had changed sufficiently, she shut off the flame, and allowed the bubbling to stop, before carefully pouring a small part of the mixture into a simple spray bottle that had been coated with a hydrophobic silica solution, and adding twice its volume of water
 
Seeing the fluid inside the transparent plastic bottle, she couldn’t help but smile. Now was the ultimate test… to see if this would actually work.
 
 
She aimed at a small wooden doorstop, and squeezed the sprayer. Immediately, a thin pink mist enveloped the doorstop.
Charlie’s cautious expression slowly turned into a wide, satisfied smile as the solution took effect before her eyes: The doorstop was shrinking! It became smaller and smaller, until finally it stopped at roughly 1/6th of its previous height. As soon as this happened, the brunette stepped towards her door, opening it slightly, and stuck her head through the opening.
“Maddie! Tell them I’m busy and won’t be able to say bye!”
Hearing a distant “‘kay!” Charlie stepped back into her room, looking at the remaining pure formula: Depending on the amount of water she cut it with, the capacity to which it could shrink something has limitless potential…
 
 
Maddie waved goodbye to her parents as they walked towards their car, her mom still giving her some reminders about where dinner is. When the doors to the car closed and the engine revved up, Maddie closed the front door and excitedly tiptoed to her sister’s room.
Standing in front of the white door, she smiled.
“Sis! Mom and dad are gone~!”
There was no response.
“...sis?”
Maddie stuck her ear against the door, trying to hear from the other side. But there was nothing.
Cautiously, she opened the door.
Her bare left foot stepped into the wooden floor of the room, followed by the rest of her body as her eyes darted from side to side.
“Sis? Are you here?”
Maddie noticed something strange: A spray bottle, laying on the floor.
“...huh?”
She stepped forward, walking closer to the spray bottle.
“Woah!” A sudden voice came from somewhere. Her sister’s voice, followed by a giggle. “Careful there, Maddie!”
“Huh?” The girl looked left and right again, confused. Not spotting her, she looked up, finding only the ceiling, and stuck out her hands wondering if somehow her sister had made herself invisible.
“S-sis? Where’d you go?!”
Unbeknownst to Maddie, her sister was far, far beneath her. Standing at barely a couple millimeters tall, dodging the giganting steps of her younger sister.
Colossal soles constantly slammed down on the floor as Maddie shifted from side to side, threatening to squish Charlie underneath her. Not that she was particularly worried though, she knew the substance would keep her safe from any amount of pressure that wouldn’t do any real damage to her, and the weight of her sister was certainly not it.
She didn’t want to reveal herself just yet. She was having far too much fun looking at the titan that was her sister looking around the room in confusion, each wave of her arms and legs resembling a mountain moving on its own.
Despite knowing that she wasn’t in danger, however, Charlie would’ve still preferred avoiding getting stepped on by her sister, so she backed away and towards her shelf. Getting further away allowed her to actually see her entire sister at the same time, just as she was crouching down and looking under Charlie’s bed to try to see where she was hiding.
“Are you up here?!”
Suddenly, Maddie started rushing towards the shelf. Charlie barely had time to react as two giant pale feet stomped their way to her, barely flying over her on their last step, ending up between the shrunken Charlie and the shelf.
Maddie was running out of ideas and, in the midst of her childish confusion and curiosity, tried to see if somehow Charlie had ended up on top of the shelf. Her heels rose up into the air as she stood on her tiptoes
 
 
For Charlie, this was more than just that, though. The rising of the heels that were barely a few inches away from her allowed Charlie to see the sole of her foot, all the way from the bottom of the heel to the back of the ball of her foot, being able to just barely peek at the underside of her toes.
“Woah!” Charlie whispered to herself. Looking at the tilted foot felt like looking at a strange, huge arch, like something out of fantasy, or a dream.
She couldn’t help it. Charlie stepped closer, putting herself under the heel and seeing it hover over her, shaking slightly. But she didn’t end there, she kept going.
Justifying this with the knowledge that she could hop sideways out of the way if the foot were to come down, she made it closer and closer to the ball of her foot, until eventually it was right in front of her.
The sole of her foot was still slightly warm and sweaty from having gone to school wearing sneakers in the morning. Charlie extended her hand, wanting to touch the sole as carefully and tentatively as someone wanting to pet an elephant at the zoo.
Before she could touch it though, a huge boom coming from the right diverted her attention.
“Oops!”
A giant book on organic chemistry fell on the floor, opening itself. This distraction, for a moment, caused Charlie to hesitate to move. And as she’d come to know, hesitation is defeat in a circumstance this precarious. The gigantic feet hovering above Charlie came down.
In an instant, Charlie was engulfed by the soft sole of her younger sister’s bare foot.
“Hm?” As Maddie put the book back in place, she felt something squirm beneath her foot, a slight tingling sensation against her sole.
“Mphh-!” Charlie was suddenly overwhelmed by the fleshy wall, immediately sticking to it. With her face right against the sole, she could barely speak.
 
Maddie sat down on her sister’s bed, crossing her leg. She brought her face closer to her foot, inspecting the sole. There, squished against the ball of her foot, there was a teeny tiny brown dot, squirming.
“Sis?!”
Using the underside of her right index’s nail, Maddie scooped up her sister, bringing her towards her face.
“Is that really you?!”
 
Charlie stumbled to her feet, the rapid movements making her feel light headed. She looked towards her younger sister, and was immediately met with the sight of a colossal pale blue eye, staring at her.
“...Ta-da!” Charlie extended her arms, giving a half-smile.
The sound of her voice confirmed Maddie’s suspicions. That really was her sister!
“W-wow, sis!” Maddie quickly placed Charlie on the palm of her other hand, trying to place her somewhere more comfortable than the underside of a fingernail. Her eyes glowed with excitement, and her leg started subconsciously twitching.
“H-how did you get so small?!”
Charlie pointed to the spray bottle on the floor. “I’ve been working on that formula for a few months now! I knew you’d like to see it in effect, hahah…”
Maddie was barely listening. She stared at her minuscule sister on her palm like it was the most exciting thing in the world. She understood why Charlie said it would let her create toys… her sister was perfectly toy sized!
Then she quickly remembered where she found her.
“Oh! I-I’m sorry for stepping on you! I didn’t know where you were! I hope it wasn’t painful down there…”
“Don’t worry about it…” Charlie admittedly didn’t love being squished against the bottom of her sister’s foot, but she didn’t want to upset Maddie after seeing her so happy. “It was… comfortable, heheh…”
“Was it?”
The slightly confused Maddie was about to ask a follow up question, when both of them were suddenly interrupted by the sound of the front door closing, followed by the sound of coins jingling.
“...what was that?” Charlie froze.
Maddie quickly ran to the door, opening it slightly and peeking at the sight of a familiar arm placing a set of keys on a table.
“...it looks like mom forgot something?” Maddie’s fingers curled slightly, partly covering Charlie.
“Oh no… is she coming here?”
Maddie closed the door. “Yep… looks like it.”
“Maddie, mom can’t see me like this around you, she’ll think I’m being irresponsible, a-and she won’t let me work on these things at home anymore! I need you to hide me somewhere!”
Maddie got nervous. It wasn’t often that her sister spoke so seriously, and at her age the worry of someone she trusted transferred right to her.
Hearing the footsteps approach and wanting to keep her sister out of trouble, Maddie was forced to think quickly. And under pressure, she never made the best choices…
“Quick!” Charlie kept glancing at the door, then back at her sister.
Maddie made a decision.
 
Charlie felt herself being flinged towards Maddie. The giant palm she was standing on suddenly tilted forward, sending her almost weightless body flying towards Maddie’s face.
At the same time, Maddie’s head moved up, ready to “catch” Charlie. The older girl quickly realized what Maddie’s intention was as a pair of thin lips started entering her field of view.
 
Everything seemed to move in slow motion for Charlie as she saw the pair of lips slowly part. A few strings of saliva stretched and broke as two rows of white, teeth were revealed from under the lips. And beyond them, and awaiting tongue adjusted itself in the cavernous mouth, quivering reflexively, as Charlie was sent straight towards it.
 
 
Before even reaching the lips, a blast of hot air hit Charlie in the face and surrounded her body, slowing her down slightly. Maddie’s exhalation, involuntarily overwhelming her senses with the admittedly mild scent of her sister’s breath and, more importantly, the extreme warmth and dampness of her mouth, a taste of what was to come.
Maddie extended her tongue, not wanting to “miss” in tossing her sister into her mouth like a tiny piece of popcorn.
When she felt a tiny bit of pressure hitting the side of her tongue, she quickly retracted her tongue back into her mouth, sealing her lips, and going back to face the door with a nervous expression.
 
 
Charlie hit the sticky, firm yet squishy surface of her younger sister’s tongue. Surrounded by tastebuds slightly protruding outwards and immediately soaked in the slight film of Saliva in Maddie’s tongue, she quickly attempted to stand up, falling back down but at least flipped over, allowing her to look above her, where she saw the impressive sight of Maddie’s front teeth from underneath. They certainly looked like they could crush her in an instant, even with Charlie fully knowing that she would be ok if Maddie accidentally chewed her.
But she didn’t have a lot more time to think about this view, as the tongue retracted into her mouth.
Light quickly dimmed in the mouth as her sister’s lips closed behind her. The atmosphere changed radically as soon as the tongue settled within the maw and the ruush of getting her hidden faded, allowing Charlie to feel every odd detail of being inside someone’s mouth. It was hot, wet and slimy… but it was also oddly cozy. It was just a bit too cold outside, so the feeling of warmth, especially emanating from her sister, made the slimy interior just a bit homey.
 
 
For Maddie, however, there was little time to appreciate the interaction as her mom walked into the room, looking for something.
“Oh, hey sweetie. I just-”
Maddie was already visibly sweating. She held her hands behind her back, pressing her lips against each other as hard as she could.
“...is something wrong?”
Not wanting to speak with her sister in her mouth, Maddie shook her head left and right, getting some hair in her face.
This movement turned out to perhaps have been worse than talking though, as the aggressive shaking ripped Charlie right off the part of Maddie’s tongue that she was sitting on, throwing her all the way to the other end of the mouth, causing her to hit the inside of Maddie’s left cheek and slide down towards her teeth, where she ended up in the precarious position of being between her lower gums and her cheek.
Maddie quickly noticed that she no longer felt Charlie in her mouth after shaking her head. This brought her another wave of panic and worry that she felt forced to power through as her mom looked at her more and more suspiciously.
“...I had forgotten my jacket in Charlie’s closet.” Her mom spoke with a tinge of suspicion on her voice.
“...Wasn’t your sister supposed to be here? Where did she go?”
 
Maddie’s upper back slowly dampened as her mom put more and more pressure on her. She didn’t want to speak, especially not now that she didn’t know where Charlie was in her mouth, but she had no idea how to end this conversation without speaking. Still keeping her lips shut, she used her tongue to prod and poke at parts of her mouth, hoping she’d find Charlie.
“What do you have on your mouth?” The voice of her mom almost spooked Maddie.
“Uh, n-nothing, see? Aaaah~”
Maddie knew her mom wouldn’t see Charlie in her mouth even if she was right there, and the last thing she wanted was for her to get a closer look. She closed her fingers behind her back, hoping she wouldn’t get caught.
“Alright… well, wherever Charlie is, tell her to clean up properly next time” She pointed at the tipped over spray bottle. “None of us would know which of that stuff is dangerous except for her.”
Picking up her coat, Maddie’s mom walked away, closing the door behind her.
Maddie sighed. She had succeeded in keeping her sister safe…
Wait. Where was her sister?
 
Charlie attempted to climb up Maddie’s tooth, but the surface proved far too slippery. She fell back to the bottom, landing on a puddle of saliva that reached up to her waist.
“Ugh, now my pants are completely soaked…” Charlie looked at her legs, noticing her socks had fallen off her at some point. “...and I don’t think I’m getting those back.”
 
Suddenly, a colossal serpent wormed its way towards her. Maddie’s tongue slammed against the roof of her mouth, under itself, against her teeth, everywhere in her mouth in an attempt to find Charlie, Until finally, it swept through her teeth, and behind them. Charlie was picked up by the humongous tongue once again, ending up in the middle of her tongue.
Then, everything started to move again. Her ears rang as Maddie spoke, also causing the tongue to shake and shift, though thankfully not enough to cause her to be sent flying again. Then, as Maddie opened her mouth, Charlie expected to see a finger coming to look for her, but instead through the once again separated lips she spotted… her mom?
Realizing Maddie’s attempt at keeping her hidden hadn’t ended yet, Charlie ducked as well as she could behind a tastebud before the mouth closed again.
 
It’d take a few minutes for Maddie to confirm that her parents had left again, this time for certain, and decide to go to the bathroom, opening her mouth.
Once again Charlie was surrounded by light. Past the slightly gapped teeth, she saw her sister’s face, attentively staring at her own mouth, trying to spot Charlie.
 
Charlie stood up, waving her light arm. Cozy as the mouth was, if she stayed any longer all of her clothes would be completely ruined.
Maddie quickly spotted Charlie. However, before she could pick her up, a thought entered her mind. There wasn’t any pressure anymore. Her mom had left. She could go back to playing with her sister and her sister’s new height if she wanted…
And with a bit of playfulness back in her, seeing her sister in her mouth was certainly… fun. She was so minuscule that whenever Maddie moved her tongue, Charlie was forced to be dragged along. She could end up stuck between her teeth like a piece of food, and…
 
“Chahlie?” Maddie attempted to speak while keeping her mouth open. “Wheh ahe you?” Maddie brought a finger to her tongue, tapping the surface of her tongue close to where Charlie was.
Charlie dodged the gigantic finger that entered the mouth, quickly noticing what Maddie was up to.
“C’mon Maddie, get me out! If you do, I promise we can play for the rest of the day, but we can’t if I’m in here!”
“Why? If the bottom of my foot is comfy, isn’t my mouth comfy too?”
Charlie quickly regretted having said that before. But what she would’ve hated to admit was that her mouth was certainly more comfortable than her foot…
“Maddie, if you don’t get me out… I won’t tell you how to use the formula!”
Maddie gasped, threatening to inhale her sister right then and there. Knowing how to use the formula… would that mean that she’d be able to shrink and grow whatever she wanted?
She couldn’t pass that opportunity up. Maddie carefully lifted Charlie up with her right index and thumb, and placed her on her palm.
“Can you… dry me, please?” Charlie moved an arm, noticing the saliva stuck between it and her tank top.
“Sure!” Maddie pursed her lips, and blew on her sister as hard as she could.
“N-not like that!” Charlie immediately fell, being almost unable to move under the hurricane-like wind pressure. “With a towel, please!”
“O-oh! Sorry!” Maddie placed her in the nearby hand towel, carefully rubbing her with it, until she was back to being dry… at least on the surface.
 
After Maddie traveled back to her sister’s room with her in hand, she placed her back at her workbench.
“Okay Maddie, I’m going to bring myself back to normal, and then we can keep playing, alright?” Maddie nodded.
Charlie looked at her supplies. They were more intimidating than she could imagine something she was so familiar with ever being, the smallest beakers dwarfing her. But of course, she had prepared for it. Walking towards a sealed jar with a serum that could nullify the shrinking effect, she spotted a small hole and minuscule funnel she had left at the bottom, usable even for someone of her size.
“I-I set it up so I could operate it at this size, so just sit tight. I’ll be done in a few minutes.”
“How long?”
“I’m not sure… about 15 minutes? I still need to cut the serum, and for that I need to calculate how much I had used to get this small.”
“Mhm…”
 
Maddie stared at her sister as she got to work. As she saw her doing all sorts of weird calculations on her head, using miniature flasks that seemed to have been made out of bent pieces of plastic, all the young girl could think of was the fun stuff she could think of being able to do with her sister when she first saw her at that size, and the excitement of seeing her in her mouth after her mom had left…
Subtly, Maddie moved her arm down towards the floor. Still staring at Charlie, she felt the floor until she spotted it.
The spray bottle.
Charlie didn’t notice the shift in movement, too busy getting the serum ready. Whenever she glanced back at her younger sister, she’d be reminded of just how overwhelmingly huge even someone as small as her looked at Charlie’s size, the sheer sight of it being enough for her to not notice if she had moved.
She kept working, and Maddie kept scheming. Slowly, she raised the bottle up to her lap, clutching it tightly.. Her little smile widened more and more as she planned how she was going to proceed. When she was ready, she subtly brought the spray bottle closer to her sister…
 
Charlie, too focused on her work to notice some of her sister’s blond strands of her enter her field of view, turned around to face her, wanting to tell her that she only needed five more minutes.
But instead of the distant head of her sister beyond her table, she was met with a familiar white nozzle.
“...Maddie?”
 
Suddenly, Maddie squeezed the sprayer. She tried to hold her laughter, but ultimately couldn’t. Charlie once again started to dwindle in size, and although seeing and feeling this happen made her feel terrified, Maddie couldn’t help but see this as harmless fun. Her sister teased her plenty of times by using the fact that she was bigger, after all. How was this any different?
 
Charlie’s tiny body didn’t stand a chance. She shrunk further down, until the flasks that surrounded her resembled more distant moons than the huge buildings they looked like before. But even worse, was Maddie. As she rapidly brought her face to see Charlie’s change in size, the only thing that Charlie could see was a pair of lips, in the shape of a gigantic toothy smile
But this was no ordinary smile. It was written into the sky. Charlie became small enough that her previous size would look to her just like Maddie did before she shrunk again.
Maddie quickly lost her sister. She seemed to vanish into the table.
“Sis? Hm, I guess you’re a bit too small now!” She giggled. “Don’t worry, I know just the place to leave you. It’ll be cozy and comfy, and you won’t get lost!”
The young girl pursed her lips, and sucked air in. Immediately, lots of microscopic particles of dust rushed into her mouth, and among them, trapped in the gust of wind, was a minuscule, nearly invisible teenager, who deeply regretted having shown her little sister her shrinking formula.
 
Charlie disappeared into Maddie’s mouth as the little girl sealed her lips. She accumulated some saliva in her mouth, and gulped down.
Looking down at her own body, Maddie patted her stomach.
“There you go, sis~! Now you’ll be safe in my belly, and I can have more fun with your spray bottle!”