Melody picks up the discarded clothes and runs up the stairs, clothes in one hand and your tiny body in the other. As she reaches her bedroom, she enters, tosses the clothes into a corner, then closes and locks the door. "Two questions before you take your turn, Melody," you say, "first, how big am I right now, and second, do you have a vial that grows me back up?"
Without a word, Melody turns and places you gently on her desk, then removes a ruler from the drawer and measures your height. "According to this, bro, you're almost exactly a quarter-inch tall. And yes, I do; in fact, I've got something even better that i think you'll like. But first, take off those swim trunks."
You take off the trunks, and stand naked on the desk looking at your sister's naked body. As she steps up on her chair and reaches for the shelf over the desk, stretching her body, suddenly you see her not as your sister but as a beautiful female, with pert breasts, a flat abdomen, and wide hips, and you feel yourself becoming aroused. Then Melody steps down with something in her hand.
"I guess this is the best time to give one of these to you, Alex," she says, and puts the FitBit-sized red wristband on the desk next to you. "Just touch it." As you do, it shrinks, winding up at a size that fits your tiny arm well, and you put it on. Tapping it, you see the screen light up, displaying four icons: a microphone, an up-arrow, a down-arrow, and a red asterisk. Displayed between the arrow icons is "0.25in," which is obviously your current height.
"This is probably a waste of my turn, but I dare you to figure out how the band works," Melody says. Looking at her, you see that she is now wearing a yellow band, which gives you an idea. You hold the up-arrow icon on your band, and the display changes until it reads "36in," and then you tap the red asterisk, and you find yourself growing; you stop at what seems like three feet tall. At that height, you can safely climb down from the desk to the floor.
"OK, are you ready for your turn yet?" Melody asks. You shake your head, saying "Not yet; I'm still figuring this out." You experiment by growing and shrinking yourself a bit, then you try swiping the red asterisk icon...
And it turns yellow. This could be interesting, you muse. The height indicator now reads "56in," and you know that Melody is 4 feet, 8 inches tall, and your guess is that you are now controlling Melody's band. So you hold the down-arrow icon until the indicator reads "2in," and you tap the yellow asterisk. Immediately, Melody begins to shrink, and gets a big smile on her face as she does. "I knew you'd figure it out, Alex!" she cries happily.
Now for the really fun part, you think. Swiping back to the red asterisk, you hold the down arrow until the display reads ".015in," which if your math is right will be about one-sixty-fourth of an inch, or a quarter-inch relative to the two-inch-tall Melody. You step very close to your tiny sister, and you tap the asterisk and begin to shrink, moving toward her as you do so. As you continue to shrink, you say, "Melody, I dare you to let me play on, around, and inside your vulva, and whatever is beyond it, and help me play when I ask you to do so." By the time you are finished speaking, your eyes are passing her breasts as you shrink, and you notice that her nipples come erect.
As your height continues to diminish, Melody grabs your shrinking body, holds it to her own, and lies down supine on the floor of her room; as you finish shrinking to a quarter-inch relative to her two-inch body, you find yourself on her abdomen, just above her well-trimmed pubic area.
"So how would you like me to help you play, Alex?" Melody purrs. "Tell me what you want to accomplish."
"First, I want to get you positioned so all this will work, so I will need you to put your legs up and leave me just a little room to get between them. Then I want to get you going," you say, "so I want to rub your clitoris until you start to get pretty wet, and maybe get you to come once or twice before I go further. Then I want to stand on your inner labia over your vagina, and then have you open your legs really wide so that I fall into you. Once I get into your vaginal vault, I will find your g-spot so that I can make you come a few more times.
"Lastly, I will let you know when I'm working on making you come the last time, so that if you want you can shrink me down again so that your cervix can suck me in, if you'd like to know what it feels like to have another person inside your uterus."
Melody grins and says, "So I'm going to be pregnant with my big brother, eh? I think once you're in my womb, I'll grow you up to four or five inches so that I can feel you moving around in there."
So it all happens as you describe it. As you rub Melody's clitoris, she begins to moan, and her entire vulva reddens and gets warm, and slowly her lubrication seeps out to cover the entire area. Her orgasm, when it hits her, feels like an earthquake to you at your almost-microscopic size; after the second orgasm, she moves her finger to her clitoris, pushing you to just the right spot above her vagina, and opens her legs wide; you drop into your sister's most intimate orifice, your tiny body disappearing into the two-inch-tall body of your sister. What you didn't expect is that, as your sister felt your body being drawn into her, that she would orgasm again, squeezing your minuscule body in an ultimately intimate embrace, before relaxing and letting the normal waves of muscle contractions draw you the rest of the way into her vagina.
As you arrive in her vagina, dimly lit by the reddish light which penetrates her tissues, you find there's not enough light for you to find her g-spot by sight, so you tap the microphone icon. "Melody? Can you hear me?"
"I... hear you... Alex..." you hear her pant.
"I need you to give me feedback for where your g-spot is so I can make you come again," you say.
"Don't worry... about that," she says, "I'm already... taking care... of that. Hold on," and as you watch, everything around doubles in size, then doubles again; obviously, Melody has shrunk you down. Melody continues, "I'm about to come again... so get ready."
The fluid level in Melody's vaginal vault, previously up to your waist, now seems 10 feet deep and rising. As you watch and tread "water," you hear a deep, titanic moan, and the walls of the chamber buck and flex. The cervix, the entrance to her uterus, begins to dip down to the fluid and start sucking it, in anticipation of the semen expected during sex. But all that is available to suck into her hungry womb is her lubricating fluid...
And your tiny self, which is quietly consumed by her reproductive organs, disappearing without a trace.
From your point of view, it is like being submerged in a log flume; as you exit her internal cervical os, the fluid pressure actually makes you momentarily airborne, and you slide along the back side of her uterus and slowly come to a stop.
You tap the microphone icon, saying, "Melody, I think I'm inside your uterus." There is no response, but as you look at the band's display, your height indication increases until it reads "0.063in." Clearly Melody has grown herself back to normal height, and being inside her you have grown as well.