A while back.
Your little sister frowned as she watched her three best friends travel upstairs with her older brother. Using a magical doll, he was able to make them all a bit older.
After holding he doll for several minutes, venting with anger, your little sister tossed her teddy bear, how dare her friends betray her like that, and how dare her older brother ruin her slumber party!
Just then she heard a small knock from the front door. Thinking that it might of been her mom returning home after sending her own perils, she hastily to open the front entrance. Who was behind the door was no her mother, but rather an old man dressed old fashioned. Staring agape at the old man as she watch him smile as he lowered his hat.
"Excuse me young lady, was this the household that had recently purchased the grow up voodoo doll?"
Your little sister recognize what he was referring to and shook her head in agreement.
"Excellent! My name is Merlin, and it just so happens that my shop was having a special deal today. With every purchase of a grow up doll, you also get the grow down doll as well, and vice versa." The old man then drew a similar doll in his hand. It looked familiar to the one her brother had, but it's limbs were stubbier, and it's stature was overall smaller. "Just like the grow up doll, you will need to provide this doll with the hair of the subject, even just a single strand of hair would work. Then reciting the magic words 'Age contra, transformatio' they will begin to regress in age. Of course to stop this transformation, you must say 'processus claudum'. Be careful going too young, you might reach a point of no return." The old man warned looking down at the little girl. "I would advise not using this doll on ourself young lady, for you don't have much years to even give up!" Chuckled the old man. "The grow up doll would better suit someone of your... stature." With that the old man handed your little sister the grow down doll. Waving good bye he proceeded to vanish.
Your sister stared in awe, she didn't really understand what the old man was saying, but she knew she had a doll of her own now. Feeling a bit empowered, she decided to show her 'friends' the new doll she had as well. Waddling up the stairs she made her way slowly down the hall.
"Wow! You two are so BIG now!" She heard a unfamiliar voice holler from her older brother's room. Peeking inside from the crack of the slightly opened doorway, she couldn't help but gasp at the sight before her. Inside her brother's room were two grown women. One of the was a blonde wearing a pretty dress, she had big boobs, and a big butt. The other was a red-headed woman wearing a tight tank top and running shorts, she had even bigger boobs, and a big butt as well.
Your little sister recognize these two women as her friends Jessica and Rebecca all grown up. She couldn't help but marvel at their adult forms. Allison however, still looked the same when her brother took them upstairs, the only difference was that she was now wearing an oversized shirt.
"Annos progressum, transformatio" she heard you say, silently repeat the words herself.
She watched with wide eyes as Allison proceeded to stretch taller into the air. Your little sister's mouth gaped watching the brunette's bust and butt fill out like a balloons.
"I feel... so... Fucking strong!" The growing teen groaned, causing your little sister's body to trembled. To think that tiny Allison would become so powerful... she had to get her hands on the grow up doll herself! But how could she? A tiny little girl like that was no match for four grown ups.
With that, your little sister watches as her three friends surrounds you, causing you to drop the grow up doll unknowingly. One thing lead to another, as she watched them pushed you down onto the bed. Suddenly the grown woman began to undress.
"Why are they getting naked?" Your innocent little sister asked herself as she continued to watch the naked ladies pull off your own clothing not to long afterwards. With that see then watched her friend Jessica climb onto your lap, shaking her big butt up and down. Your sister having no concept of sex, couldn't quite conceptualize what was transpiring before her. All she knew it was quite humorous watching Jessica's big booty jiggled as she played her weird game.
Jessica soon huffed as she pushed her brother into the bed, lying flat as her butt jiggled harder. Rebecca and Allison stood by Jessica, their backs turned away from the door. Your little sister knew this was her chance to pick up the grow up doll on the ground. Sneaking in, she quickly grabbed the voodoo, turning around to head back out.
"Ohh.... FUCK!" She heard the blonde woman yelped. This cause your little sister to jump, thinking that she had been caught. Turning her little head around, she only saw Jessica clenching her ass cheeks repeatedly as her body shivered. Her own brother's legs wobbled, as his toes curled.
"Grown ups are so weird" your little sister scoffed as she waddled out of the room. Now possessing both dolls, you little sister couldn't wait to try the grow up doll for herself. Looking for someplace a bit more secluded to continue, she made her way inside her parents' room. Looking at the floor, she notices the discarded toddler clothes her friends once more. Standing by a mirror, she transfered the three strands in hair onto the grown down doll. It amazed her when the hair snapped on like magnets. Rustling through her own hair, she finally got a loose strand, as she snapped it onto the grow up doll.
"Annoso progrenum transmato" she slurred. Waiting a while, she notice nothing was happening, "annos... progressum transformatio?"
Suddenly she gasped as her whole body shook. She watched as her little body began to stretch taller before the mirror in front of her.
"It's happening! I-I'm growing, I'm growing up too!" Your sister smiled as she watched her limbs lengthen. Her body quickly transformed from a toddler to a kid. Her clothes were started to pinch into her skin.
"Ow... Ouch! My clothes... Uhh... I need to stop for now... What was it... Oh yeah... processus claudum!" she rambled. Your sister gasped as the sensation stopped.
Looking at the mirror was no longer a toddler looking back at her, but a perky preteen in tight clothing. Yanking the tight garments off, your sister stared wide eyes at her new figure. Looking at her chest, she can feel her breast coming, and twisting around, her butt was definitely a bit rounder tan before. "This is incredible!" She smiled.
Just then she remembered the events that transpired shortly beforehand. Her face suddenly contorted in disgust as she realized what Jessica was doing with you with a new sense of clarity. "Oh my God! That is so GROSS! Why would she do something like that... with HIM!" Your sister couldn't believe why she didn't understand what the two of you were doing on the bed just moments before. She can now clearly recall seeing your schlong enter her pussy, causing her to spit out in disgust.
"I can't believe him! Turning my friends into SLUTS!" Looking at the grow down doll on the ground, she smiled. "I think they all had more than enough fun... but first, I want to finish my own growth." With that she recited the magical words as her body began to tremble once more.
Smiling, she watched her womanly assets blossom before her eyes. Her breast swelled into sizable lumps, as her body curved out. Her hips widen, as her ass pushed out."Mmm... not bad" she purred as she clasped one of her boobs, satisfied by it's weight. Feeling she had grown enough, you sister recited the stopping words as the sensation ended.
Twisting and turning her adult body, your sister was rather proud on how sexy she grew up to be. She once again thought about Jessica riding your cock, while she was still a bit disgusted, her vagina began to quiver. She couldn't help but massage her new adult genitalia, relishing in the pleasurable sensation it provided. Squeezing her hard nipples in one hand, while fingering her wet pussy with the other. Overwhelmed, you sister collapsed onto the nearby bed. Her thoughts became stronger as she remembered Jessica shaking her ass harder, replaying the orgasm she witness over and over again.
"Oh, God!" Your sister huffed as she arched her lower back up. Suddenly, her body quaked as she reached her own first orgasm. Trembling from her intense climax, your sister hears another cry of pleasure coming from the room next door. "I think it's time I paid my friends a visit." She smirked. Lower her shapely longs legs off the bed, you sister opens your mother's closet, searching for a more suitable attire to gown on her new curvaceous figure. Finding a sleek blue dress, she grinned as it fit her perfectly.
Heading out, she peeked into your room once more. This time she saw Rebecca laying face down on you bed, her giant ass up as you rammed into it repeatedly. Glancing around the room, she saw her friends Jessica and Allison standing not to far away. As she watched Jessica finger Allison, her own pussy began to throb. Looking down at the grow down doll with it's three strands on hair: gold, brown, and orange. Your sister remembers the words the old man had told her, and smiled "Age contra, transformatio" she mumbled quietly.
She watched as the girls froze, trembling as their body began to regress. Her brother though, was woefully ignorant, still pumping his dick into the red-head on the bed.
"OooOoOh! Your dick is so BIG!" Rebecca's voice vibrated.
Scanning the room, your sister watched as the former adults plummet back into teenager. Their incredible figures were slimming down, as their heights began to inch lower as well. Finally she watched you yank your dick out of her friend. "Looks like he's finally noticing." She grinned as she watch you twist and turn in confusion.
As the girls return to being toddler, ducking under your bed covers. Your sister smiled as she saw you make towards the doorway...
Kicking back to present time.
"Processus claudum."
Your sister laughed as she looked at the little 5-year old boy sitting inside pants much to big for him. The little girls on the bed stared with wide eyes and open mouths.
"Look! He's small like us!" Jessica cried out.
Your sister continued to giggle as she looked around the room.
"What to do now?..." She grinned.