Ellie immediately started wiping her butt off to get rid of Katie's ass sweat. Katie just laughed, having enjoyed the double fart they just gave you. To her it was hilarious, but you didn't find it as funny. You couldn't get the awful smell off you, and now you were covered in a fresh batch of anal slime. The stench made your stomach turn, you almost wanted to throw up. In your time of unrivaled despair your sister was there for you, readying her ass for even more torture.

"Oh brother" she cooed.

"Gwen... no more..."

"I can't hear you down there "big" bro! Your voice is too tiny!" the red-haired goddess taunted.

Her gigantic ass squat over your body, her spread cheeks revealing her throbbing poophole.

"Don't!" you wheezed, your voice barely making a sound.

Slowly she lowered her giant ass down on the bed. The shadow grew larger and darker until the entire weight of her body was smothering you. The bed had some give to it, but it didn't matter, your sister's ass was completely flattening you. It was impossible to move a muscle, your own younger sister's butt was too big and heavy. Just by simply sitting she had completely dominated you. Thanks to the light being gone you couldn't see, but you felt her body's warmth. Rubbery hot skin twitched at your chest. It was oily and round and a bit sticky. It had to be her anus, she lined it up so its smelly folds would be planted right on top of you.

The anus pressed hard into your body as your sister let out a grunt. Her tremendous ass unleashed a mighty fart, pummeling you underneath her shithole. Katie and Ellie laughed wildly, cackling at you being farted on. Hot meaty gas gushed from your sister's tight hole, burying you in a dank pocket of her fermented scent. A splattering of wet ass juices launched from her asshole, soiling both your face and the bedsheets. The anus rampaged on your chest, battering your ribs as the spewing gas sought to escape Gwen's crack. Small puffs tooted from the sides of her cheeks while the majority of it remained trapped under her giant crevice. You cried at the center, in the middle of your sister's concentrated death cloud as her anus pumped more gas into the mattress. A sigh of relief escaped her lips as she let it loose, enjoying the pressure from her butt being released.

"Ahh..."

Her fat ass leaned back, and her anus slid off your chest and onto your face. The hole was still gaping slightly and extremely hot after letting out her fart. The relaxed circle of meat let your head sink a little into it, and you tasted the vile mucus lining her inner rim. You writhed in disgust, trying to shimmy yourself loose but that only made her body more aware of your actions. Your younger sister's greasy anus clamped shut on your head, clenching with an iron grip. The sticky warm folds of her butthole pushed your cheeks together, messing up your face. She noticed how far in you were, father than ever before. It made her ass tingle, and her hole started to chew rhythmically on your skull. Waves of pleasure washed through her young body, yearning for more of this weird sensation.

"Ohhhh... he feels good..." she moaned.

Katie and Ellie watched your sister start to really immerse her self in your torture. They began to whisper for a brief moment, nodded to each other and finally Katie said something.

"Gwen... we were both thinking. Since you invited us over to have this slumber party together he should go inside your ass first. He's your brother and all so you should be the first to use him like a buttplug."

Gwen broke out of her trance at that moment, her red hair flipping as her head swung around.

"Really? You mean it?!" she said with a beaming smile.

"Yeah, besides, Katie and I can use him tomorrow.  We are gonna have such a fun weekend!" Ellie said.

Gwen's tight pucker separated from your face with a wet pop. Her huge ass lifted back into the sky but you weren't going to be apart for long. She was just loosening herself up, prodding the entrance to her bowels with her finger so it would be ready for you. You were both going to be together again real soon, and closer than ever before...

Katie's giant hand picked you up, she was giggling at what she was about to do. Ellie hugged your sister's backside, pulling her plump cheeks apart. You were presented with a clear view of your little sister fingering her butthole.  The digit sunk into the slowly loosening opening, squelching from the juices inside.  Removing her finger, you stared into the abyss of Gwen's asshole, and it stared right back at you. She was bent over and waiting for her friends to push you in. Huge and round, you had trouble imagining her butt about to swallow you. More like you didn't want to imagine it, but it was a reality that you were going to face regardless. The juicy anus throbbed and puckered at you, eagerly waiting to devour you whole. Her butthole freckle danced around with each subtle anal contraction. Your throat was just slick enough with awful slime that you had the power to speak again. You yelled with your loudest voice, begging Gwen not to send you inside her.

"Gwen! Please! I'll do anything you want! I'm serious! You can make me do all your chores for a month- a year! Anything! Just not this! Please for the love of God don't put me up your dirty asshole!"

Your sister's face peeked at you from between her legs, blushing bright red. Her hand was rubbing her crotch and she was panting heavily.

"Sorry bro... right now, I just really want you to go inside my ass."

Katie's hand moved you forward. You screamed louder than ever before, terrified as the giant twitching asshole grew closer. Your sister's anus was ready to eat you alive, hungry to feel your flailing body inside hers. Punching and kicking did no good against Katie's hand, it was too strong.  A quick succession of beeps sounded nearby.  You heard the echo of the girls' laughter ringing in your ears as you looked to your left and saw Ellie holding up her cell phone. Another recording was going to be added to their collection.  Your mind raced to all the times Gwen anally humilliated you.  You have become a little too aquainted with your little sister's butthole. She tormented you with it for so long, but now you were about to get the most intimate experience with it.  Giving the anus one last glance, you closed your eyes tight and braced yourself for a tight insertion.  Face-first she pushed you into Gwen's slightly gaping hole, mashing your mouth into the dead center of the ping ring. The tight orifice offered resistance at first but then gave way and let you push through. Your sister's hot innards spread open to let you slide in, accepting your body into hers. She moaned loudly as Katie inched you inside.

"AAAAHHHHNNN!!"

Hot gooey juices slathered all over your body. Your sister's bowel walls squeezed lovingly, tensing up and kneading you into their flesh. You felt clausterphobic inside her meaty tunnel, the hungry girl meat smothered you from all sides. Gwen moaned again and her ass sucked you up, pulling you deeper inside her depths. Your tiny feet slipped from Katie's fingers and the asshole shut tight, leaving you lost in the darkness. Worst of all was the smell, the wretched scent of your sister's ass was like breathing in her farts endlessly. The putrid stench was making you dizzy, like the constant smell of shit fumes was fogging up your head. Gwen's heartbeat was pounding, thumping into your body through her walls. You felt exhausted and finally passed out, letting the darkness take you. Your transformation into a toy was complete, a human-shaped butt plug inside your little sister's anus.

"How does he feel in there?" the tomboy Katie asked, her face blushing through her tan.

"Mmmm, real good...My big brother is the best butt plug." Gwen moaned.

She patted her hand on her ass cheek, concentrating on how you felt inside. You had stopped moving so you must have passed out. It made sense, you had just gone through a lot. Even though you were just acting as a tiny blockage in her ass, just knowing that it was her own older brother inside her sent Gwen over the moon. She had successfully made you into her ass toy, and now your purpose was to act as her butt plug for as long as she wanted.

"Yeah... he can stay in there for a while" Gwen smirked.

"It's what he deserves for being such a pervert" Ellie stated.

"How about we order some pizza?" Katie said. "I know this sounds weird, but all that farting made me hungry!"

"Yeah me too." Gwen agreed. "I know! Let's go find my brother's wallet, it can be his treat!"

"Hee hee, good idea!~" Ellie giggled.

The three of them fished around in the pile of your clothes, left from when they shrunk you. Sure enough in your pants pocket was your wallet. They laughed and continued to party, now free of any supervision. The girls watched Ellie's recording as they feasted.  It captured the hopelessness in Tom's eyes perfectly. Gwen gave her ass a heavy squeeze, delighting herself as she felt it chew on your firm shrunken body. She planned to keep doing this every so often for the rest of the night.  You never were more than a mere toy for your sister's enjoyment, she planned on bullying the babysitter all weekend.