Sarah let out a cry of pleasure as she felt something hit against her sensitive pussy lips. She was already wet down there from her working on her nipple but this was irresistible.

"Ugh... and in my sister's house..." she moaned to herself. "This is... this is so dirty... I can't believe I'm doing this... but at this point I can't help it!"

pulling up her dress to reveal her panties, she slid her hand under the waistband and along her bald pubic mound. Once she had slid them over her twitching clitoris she proceeded to push her well manicured slender fingers deep inside her unaware of the passengers she was taking with her.

"Ugh! Sam!" she panted between pumps with her fingers. "This is my vengeance for abandoning me today! You're gonna have your little sister's womanly juices all over your boyfriend's bathroom floor!"

As she continued to stroke herself and rub her nipple simultaneously, she felt as if her vagina was on fire. She had never been able to feel sensations this deep with just her fingers before. Maybe she was coming across a new fetish!"

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"I repeat... this is NOT a side I wanted to see of my little sister..." Sam grumbled from her seat. We sat back watching as two massive fingers continued to pound away at our only exit.

I had thankfully managed to drive us deep enough that Sarah's fingers couldn't reach us, but so help me the girl had long fingers. We were practically parked against her cervix to avoid being crushed. Her nails were covered in pink nail polish with gold glitter tips which had begun to stick to the walls. It made me wonder how she was going to react when she found out her fancy manicure was being ruined by this.

"Knowing she's related to you... our only option is probably just to wait until she's done..." I replied trying to lighten the mood a bit.

"Mmm." was the only grunt I got in response.

Turning to Sam I saw her looking up frustrated at the massive fingers which blocked our way. Sarah's love tunnel was surprisingly different from her sister's which made me wonder how much they varied from person to person.

"Say Sam?" I asked apprehensively. Today was supposed to be our anniversary, so I felt horrible that she got dragged on this crazy adventure.

"Hmm?" Sam replied disinterested.

"You know how we have our valentines day special for couples right? The one where we let them all have sex in your vagina while you orgasm?"

"Mmm" Sam replied still equally frustrated and disinterested.

I took a deep breath before suggesting the next part.

"Did you ever.... Did you ever want to try it yourself?" I asked nervously.

Sam turned towards me with a look of disbelief on her face.

"Did you seriously just ask me if I wanted to have sex with my boyfriend in my little sister's pussy??" she cried out.

I flinched defensively blushing at what a ludicrous thing I had suggested.

"Look, I know it was a bad suggestion." I defended. "I just thought this might be the only time you get to try it so I thought I would offer!"

Sam leaned back in her chair looking at the pulsating red walls outside.

"It's a horrible idea..." she replied putting the final nail in my coffin. "But... at the same time... I will admit, I've been horny for the past hour and desperately need someone to do me right now..."

I quickly turned to Sam who had leaned towards me with glossed over eyes.

"Hey Ken..." she asked putting her hands on her thighs. "Help your giantess out a bit?"

This was all the encouragement I needed. Pulling Sam into an embrace, I began kissing her vigorously as I ran my hands along her body. Sam in turn grabbed at my pants far more passionately and began stripping me down.

I gently removed her clothes noticing that her panties were already completely soaked through and then began fondling her breasts as I was kissing her. At one point I attempted to pull away, but she grabbed my by the head pulling me back into even deeper kisses.

My girl was... VERY turned on.

Now that we were both naked, we made our way outside of the vehicle where we were instantly bombarded by waves of hormones from Sarah's vaginal fluids. The aphrodisiac effects of this was something I was already familiar with, but for Sam this was her first time, and she was far from immune to it.

She began kissing me all over as we were thrown against the soft wet walls of Sarah's vagina by her internal convulsions. Sarah's wet liquids covered us lubricating us and making us all the more passionate.

No longer able to hold back, I began having sex with Sam sliding easily into her pussy with the mix of her and Sarah's juices. We moved to the rhythm of Sarah's fingers and the movements of her vaginal walls turning us on harder than we had ever been before.

It was an amazing set of intercourse and no sooner had we finished in each other, than Sarah orgasmed blasting us and the vehicle out of her young pussy along with her juices.

We found ourselves on the tiled floor of our bathroom between Sarah's legs sitting in a puddle of her womanly juices. Above us was the twitching lips we had fallen from and in front of us was the massive canyon of her butt cheeks spread apart slightly as if asking us if we wanted round two.

Sam and I both refused the invitation, and instead made our way back to the vehicle leaving Sarah to lie on our bathroom floor panting in private.

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"I'M GONNA MISS YOU SO MUCH SIS!" Sarah cried out giving her sister a giant hug.

After we had taken a quick shower, we returned to normal size and met up with Sarah who had become surprisingly bashful. We apologized for our absence, I said it was my fault as something work related came up I needed Sam's help for, and we proceeded with our visit.

Sam was a little awkward next to her sister after having seen so many new sides of her, but having not known what their relationship was like normally it could have just been how they normally were.

Now we were saying goodbye to Sarah, wishing her luck in college and telling her she could stop by any time (but maybe call first next time.)

Sarah walked away leaving Sam and I alone in the house once again.

"You know... if you ever want to tell your family I'm willing to take the blame for everything..." I replied to Sam as she shut the door.

"That's okay.." Sam replied with a satisfied smile. "I like it better this way."

Wrapping her arms around me she gave me an incredibly long and deep kiss before pulling back and admiring me with passionate eyes.

"Your tiny adventures are MY private fun time and I don't want to share you with anyone else!"

I involuntarily blushed as Sam revealed her unexpectedly possessive behaviour.

"Umm, so... how did it feel being the shrunk instead of the giantess for a change?" I stammered in an attempt to change the subject.

Sam looked at me with an unimpressed blank stare. Reaching behind me she grabbed the shrinking device from my pocket and proceeded to shrink me to close to a mm in size. I looked up to find myself on the underside of her fingernail being brought down at high speeds along her body. The finger proceeded to take me along under her waist band and through her pubic hair until it stopped holding me directly in front of her already erect clitoris.

(Good gracious girl! You've already orgasmed 3 times today!) I thought to myself admiring my girlfriend's stamina when my cell phone rang.

"Sam?" I asked apprehensively as a shy voice responded.

"I didn't get to enjoy the tour today because Sarah interrupted." Sam explained. "I want you to make it up to me now."

With a mischevious smile I jumped off of Sam's fingernail and proceeded to climb under her clitoral hood. She had made sure I was larger than I had been during the tour so it was a tight fit, but her twitching and growing clitoris suggested she did enjoy it.

"Hey Ken?" she asked sheepishly over the phone. "I don't want you getting aroused in any other girl's vagina except for mine from now on okay?"

Again, my heart beating faster from Sam's unexpected bashful side, I didn't even need to answer. I proceeded instead to rub my whole body against her twitching clitoris which was met by sounds of groaning from her from above.

I love my girlfriend so much...