“I—I can explain!” I squeak, pulling my hand away from my penis, where I’d been jerking off for who knows how long with my sister standing there in the doorway.

“Uh, dinner’s... ready,” she says, not taking her eyes off my erection. “So if you’re done being a boy, and um...”

Her gaze raises to my computer screen, with a close-up video of a penis going into a vagina. Nothing else, just the raw, primal act of fucking.

“Wanting to fuck a girl,” she concludes, “Then come on.”

She heads out then, and I’m so embarassed my dick shrinks away like a deflating balloon. I didn’t do anything wrong, but now she thinks I’m some kind of freak. What if she tells our parents? I—I don’t think it’s bad to masturbate, but I’m just not used to this... urge to fuck a girl. What would they think if they knew?

Well, she doesn’t, but dinner’s a little more awkward that evening than usual. And that’s it, she never catches me again, and for all I know she’s forgotten about the whole issue.

Cut to a month later, when there’s a snow day, but our parents still have to go to work. I’m considering whether I want to bundle up and go out into the cold to play in the snow or not, but my sister has other ideas.

“So, we’re all alone,” she says coyly, standing before me in a dress and a t-shirt which I’ve been told is a blouse, even though it just looks like a t-shirt. “Just you and me, huh bro?”

“Yeah, it’s kinda...” I say trailing off at the thought of what we could do together.

“So, you like... porn, huh?” she asks, making the memory of what she saw me doing come rushing back.

“I uh... not... a lot?” I reply, anxious that she might learn how much I’ve been hungering to just shove it in a girl and cut loose. 

My dick’s been getting bigger over the past year, I’m growing up I guess, but now that the thing gets massively erect, I’m just having to masturbate every day, cumming hard as I can. That massive erection feels like it’s controlling me: until I cum, it’s just started overwhelming me with the urge to do it inside a girl. Like my sister. 

She would... never say yes to something like that. She’s a *girl* and I’d get her pregnant. And I’m her brother, so there’s no way, even though we’re all alone and we could totally... do it.

“It’s just so weird,” she says, swaying her hips thoughtfully or something, “My kid brother wants inside a woman.”

“I’m a year older than you,” I grumble.

“Yeah, but what’s it like, just... wanting to fuck girls?” she says unrepentantly, “You just started... looking between our legs one day, imagining... putting it inside?”

“I don’t know if I should say,” I tell her cautiously, “I mean, that’s how you felt, isn’t it? It’s not like I’m just sitting around ogling girls.”

“It is how I felt,” she says urgently, “Just didn’t know it was the same with you. I started looking at boys sometimes... down there. I... looked at your computer.”

Now I turn away from the window, giving her my full attention. 

“Sorry, I sort of got curious,” she confesses, blushing, “Y-you don’t have much porn, just some couples ffucking.”

“You looked at my *porn*?” I ask in disbelief. “Did you... like it at all?”

“...it made me cum,” she says cautiously. “Looking at those videos. Made me want a p-penis inside me. I-I wanted to be those girls.”

She walks up to me, saying more earnestly, “It just happens to me! I got this vagina that just... started wanting boys inside it. W-when you masturbate, does it get worse?”

“Does what get worse?” I ask, only having to look slightly down to meet her eyes, only half knowing the answer.

“The way you want to... put your penis inside girls,” she tells me, “And the closer you get to orgasm, the more you want it?”

I shouldn’t tell her. Should end this right here. But an undeniable thrill’s going through me, that I can talk with her about this stuff. “My erection’s getting bigger,” I tell her shyly, “In... in the past year. The bigger it gets, the more I want to put it in a girl, because I’m... getting to that age, I guess.”

She looks at me solemnly, then touches the t-shirt on my chest with the palm of her hand. “You’re taller than me,” she grumbles.

“Only a little bit,” I protest.

“I might be a really tall girl someday,” she says, leaning more against me, “But you’re gonna be taller. I wonder if it makes it easier for you to fit, that way.”

“I... suppose,” I say, awkwardly hugging her. She hasn’t so much as touched me in... well, at least since that little masturbation incident. And now she’s hugging me and... holy crap her crotch is pressed right up against mine.

She doesn’t say anything, just hugs me and grinds her crotch against me. I couldn’t not get erect! “Oh wow, you’re... swelling against me,” she murmurs, her leg wrapping around behind mine. I want to fuck her. I shouldn’t, though.

Releasing the hug, my sister modestly starts undoing the button on my pants. “What are you doing?!” I ask her in frustrated arousal, tugging my hips back but her grabby fingers hold on to the lip of my pants. “We shouldn’t... do this,” I say, but I don’t fight to keep her from pulling my pants down. She stares at my briefs, taking a long, calming breath in or something. Then she pulls down those two, groping at my penis and balls declaring,

“Oh wow, you’re so soft!”

“Not for long, if you keep doing that,” I say, groaning as the blood pumps into my penis, swelling and thickening it, and filling my thoughts with... sisters. “You really wanna just... have sex?”

She doesn’t respond at first, squeezing my lengthening shaft in her hand, then releasing it as my shaft swells outward. “You smell really good,” she says, “I don’t care if you’re my brother. I–I’m getting wet.”

That confessed, she stands up to hug against me saying beseechingly, “Just like your penis wants, right? I get really wet. I can’t help it, it just starts happening. My body’s getting ready for your... your penis.”

“My body’s getting r-ready for your vagina, too,” I tell her honestly, “You keep rubbing my... my penis with your dress. Where your vagina is.”

She gives a frustrated huff, and pushes away, sliding the hem of her dress down to her ankles, then hugs against me again, and holy crap she was not wearing panties.

“You *are* wet! R-really warm too...” I tell her, as my sister grinds against me, the both of us effectively naked from the waist down. “I can feel your... your outside,”

“Labia,” she informs me tenderly. “I can tell you all about my... my sex,” she adds, lowering her hand to grip my penis again, and press her crotch against the very tip. She’s so wet and eager as she says, “And you can tell me ungh—” when my penis just *sinks* into her wet, fleshy embrace. “All about your... your penis,” she huffs, sinking down on me. 

I’m... I’m just vanishing into her, as my sister pushes more of me up her hot, slimy tunnel. I push too. Soon as I get in her vagina it just wells up in me, and I grab her hips. It’s changing me, changing everything in my head, the deeper I get, and I want inside so bad, I let myself change to be this thing, pushing deep until our hips are grinding against each other. What... what am I?!

I feel like such a man. My penis in there feels so big, and ponderous, and powerful, it’s all I care about. I don’t care about myself anymore. Don’t care about her. All I can think of is where my penis is, and what I’m gonna do in that vagina. All my doubts and worries are just... replaced, by an urge to climax as deep and hard in there as I can. That’s what was changing, and I still pushed it inside, knowing... hoping I’d become this... this thing that wants to fuck my sister.

“Oh, I thought it would *hurt*,” she says passionately, grinding against me once before. Within her, that passage is hot and alive, *moving* around me, and *squeezing* my penis. Looking up to meet my eyes anxiously, the slim-chested girl says, “You *have* to fuck me now, right? You’re gonna cum inside?”

“I... I’m a thing,” I tell her in wonderous horror, hungering to fuck her so bad. “It changed me. All I care about is my penis now. D-did it change you too?”

“Oh god yes,” she moans, pulling her hips back and forth to gently fuck me, “I’m just a vagina now. You’re gonna put a baby in me. I don’t care if... if our parents come in. Just... animals... your penis changed me...”

“Is this right?” I ask anxiously, trying to thrust back from our awkward standing position. Her vaginal walls glide against me like silk, so much better than my rough hand. The skin of my penis can actually slide this way, not just tug back and forth!

“It feels good...” she says more to herself than to me, “It feels...” she stops hunching against my slow thrusts to look up at me again. Just the two of us standing here in the room, half naked, with my erection up into my vagina. “It feels so good, *moving* in there,” she moans, clinging to me like a lifeline, “I need to... I need to lie down.”

She pulls back then, my hungry erection crying out to stay inside, as I slide free of her labia completely, bobbing in the air. She pulls me to her room, to her bed, and I follow like a boy possessed. Was I really just inside my *sister?* My penis feels slick, chilled. I was in her vagina, and I could just put it in there, *again.*

Laying back against her bed, belly up with her legs spread before me, she says, “So, you’re gonna put a baby in me, huh? You’re a boy, even though I’m your... your sister.”

“I was inside you,” I tell her in wonder, frantically fumbling to align my penis with her presented hips, standing by the bed as I try to get that sensitive bulbous head into that amazing tunnel. I *am* gonna put a baby inside her! “It *changed* me,” I say in passion, grabbing her thighs and pushing deep, hilting my shaft in my wonderful, beautiful sister. 

I take a trembling hand away to touch her belly. Both of us are panting and heaving, not quite thrusting. Her belly flexes against my hand’s touch, as I wonder if that smooth flat abdomen’s gonna get big and round because of me. “Suppose this’s where you’re gonna get... pregnant,” I tell her feeling a deep yearning as I do so, like reverse nostalgia.

She places her hands on top of mine, pressing mine into her belly and declaring in amazement, “Can’t believe I *can* get pregnant. That... this could get big, and round, with a baby in it. I could g-give birth.”

There are tears in her eyes, when she looks up at me, standing there hip deep in her cunt, and says, “I can feel where my baby’s gonna come out. Where your penis is! You’re gonna... cum inside me. You’re gonna change me into a mom. I... I’ll hide it. We won’t tell anyone. We’ll be careful. I’ll give birth in the woods, so no one has to know. O-only you get to see... h-her coming out of me.”

I can’t answer her. Just the thought of her letting me see the baby coming out fills me with an animal hunger to impregnate this girl. My sister. Our baby could be totally retarded and I don’t care. I pull back out of her and push in, thrusting, and thrusting. She lays back while I hold her legs for support and slide in and out of her, looking between her legs, murmuring, “Holy crap, I can see *everything*.”

I feel like I’m on show, like I’m some sort of... entertainer as she gazes at my pistoning dick in adoration. I fuck her faster, and find it impossible not to slip into that ancient rhythm, that every guy who’s ever fucked a woman has known. “So beautiful...” she moans, holding her small breasts in her hands and writhing at my steady, pistoning thrusts, keeping her eyes glued to what’s happening to us between her legs.

Her hands leave her breasts then, to brace on either side of her, humping back up against me, as I hump forward deep into her. She stares dully at her fucked pelvis, as I stare fixedly down at her, fucking and fucking, so eager to cum in this girl. And her vagina just keeps getting tighter and tighter. It’s hard to fuck her, even! Is this supposed to happen?

My eagerness to cum miraculously breaks, when my sister groans, “I’m gonna *cum* you haven’t even *cum* yet.” I don’t know what it is; I just start thinking about her cumming, and then all I care about is her. She turns her head up from staring at her crotch, looking at me apologetically, saying, “I s-squeeze when it happens, don’t worry. I might... I’m gonna pee. It just happens. So just d-don’t worry, I’m okay I promise I just—! Can’t—!”

Her pupils narrow as her babble falls to gasps rising in pitch. I keep fucking her, somehow forgetting about my own climax before this flushing, squeaking female who needs to cum. And I don’t care what she does. I’m not myself anymore. I’m the boy who’s gonna do anything he can to make her climax. It’s easy. She’s so stoked by this, even my clumsy, raw thrusts of instinct push her over the edge.

Then she cries out frantically, “Go deep, go deepmmmmnnnnn–!!” and I push deep just in time for her to start bucking against me as her inner tightness turns into a storm. I can’t put words to how good it feels! The inside of her vagina isn’t just wet skin, but muscle, squeezing powerfully around me again and again, in another one of those timeless rhythms that I’m only now experiencing. Then, I notice her urine soaking into my groin.

It’s... fascinating. She lays there panting and bucking her hips, pinned by my dick against her bed, and the urine just... squirts out of her right above my dick. It pulses to the same rhythm of her vagina, then seems to reach a steady rate, flowing out of her to soak both our crotches, and her own bed underneath her.

I start fucking again, and her surprised moan is all the warning I get before her inner clenches surge in strength again, and her pee sort of increases to a spray for a moment, before going back to being this hot liquid flowing down over my thrusting penis. I don’t care. All I care about is cumming inside. I don’t care how wet she is on the outside, because I know what it feels like to have my semen spurt out of me, and I *need* to feel that inside my sister.

It catches in me like fire, and I fuck... slower, trying to stretch it out, because I don’t know how long before we’ll ever be able to do this again. My testicles are tight against my shaft, dutifully providing the sperm that will impregnate my sister, that I’m about to squirt inside her. There’s no denying it, even the slowest thrusts flood me with that orgasmic fire. “Guess I’m... gonna put a baby in you now...” I say in an almost relaxed tone.

“You’re gonna...” she says in wonder, looking from my crotch to my eyes again. “It’s happening to you?”

Tensely I nod, trying to slow but the pleasure just won’t go down. My whole penis is inside a *female*. “I’m not pregnant yet...” she coos, hugging me against her, “You’re a *male* your penis’s ready to *change* me. H-how’s it feel?”

“Tingling,” I grunt, barely pulling back to push deep again, “Flooding into me, gonna spurt hard as I can. Can’t move f-fast or I’ll...”

“I feel stretched,” she huffs, “Wet. *Deep.* My cunt’s squeezed *all around* you. Feel the head of your penis, ready to start squirting in there. My whole body’s ready, and as soon as you squirt I’m gonna have a baby in me.”

“Can’t... hold back, sorry I...” twitch twitch *twitch* I surge against her as my penis flexes with an intense spurt of semen bursting out of it. 

“I feel it!” she gasps, “Your seed’s—I feel it hitting me! You’re *throbbing.*” My whole body tingling with an electric orgasm, I’m staring down at her crotch now, flex flex flexing my penis as it fires my fertile seed deep into her belly there, and I keep doing it. 

Even as I say, “I’m—making you... pregnant,” the spurts have already eased. “Oh sis,” I say, trembling, buried inside her, feeling chills from the orgasm that coursed through me. “That was *incredible*!”

“Making your babies...” she murmurs, one hand rubbing her slim belly where my penis is, while her other presses against the front of my shaft, sliding her index finger up into her vagina alongside me just a little, her thumb pressing at the top of her vulval lips beyond that. “Felt you *throbbing* in me,” she says hotly, “That was your penis *cumming*. I can’t stop it now. I-it was so warm. I’m gonna have your baby now...”

Leaving her legs to drop down to either side of me, I hug my sister, supporting her back as she hunches forward in my odd embrace. I hold her as she works herself to climax again, until she’s yelping and falling back, twitching on her bed, as her vagina comes alive around me again. So I don’t... pull out of her at all, but I follow her forward, and push her hips with my hands and penis, climbing onto the bed with her, to actually hug my quietly moaning sister.

As if noticing my presence for the first time, she hugs back fiercely, whispering over my shoulder as her inner clenches eases, “Thank you... I feel so good, thank you... I’m flipping out and... I can. You’re... you’re letting me do this...”

“Hey,” I say softly to her ear, “Orgasm as much as you want. It’s... you’re beautiful.”

She just moans and humps against me.

...

“Man, bro. Rape is awesome!”
“Rape?!”
“Well yeah, it’s not like I ever asked you to fuck me. You just sorta did it, like some kinda *animal.*”
“You were the one who wanted it! I never asked you to do it either, so you’re the one who raped me!”
“Bro, just because you’re raping me doesn’t mean I can’t rape you back.”

...

“Honey, why are you washing your sheets?”
“Juice! Spilled some juice on them playing... video games!”