Rose does, and you gain an ally

Squeezed in on both sides by a hot, sweaty flagrant display of nubile, half-naked teenage flesh, it’s difficult to focus on which of your lovely siblings are most deserving of refreshment. You use the word lovely in the purely physical sense, because whilst you've always gotten along with Marie in the typical sibling ‘looking out for but riffing on each other’ way, your relationship with Rose was rocky at best. That’s entirely her fault of course, she just turned into a grade-A bitch since she hit puberty. She didn't used to be all that bad though - as you recall, the two of you used to get along well enough as kids until pretty much overnight, she became distant and annoying. Hormones, am I right?

Although... if you were a little more honest, she might have noticed you perving on her perky little tits and barely legal, tight little teen ass once or twice. Maybe a few times. Okay, okay! …Maybe literally every time she was in the room. You were discreet, of course (Clara would beat the shit out of you if she found out you were letching on her little angel) but come on! It was obviously her fault for wearing either nipple-pokies and cameltoe tight, skimpy slutwear or cleavage revealing loose pyjamas around the house all the time. When you can see the bottom of a pair of perfect, tight as fuck ass cheeks right there on display or braless nipple bumps under a tiny pink crop top, what else is a guy gonna do but sneak a peek? Creepy misogyny and incestuous undertones be damned, when a sex starved body full of horny hormones has barely legal tits and ass shoved in its face every day, a guy is gonna stare. That’s just biology, man.

So, what used to be innocent tickle fights and lounging around playing comfy video games together quickly became rolled eyes and insults - then sneers and texting on her mobile behind doors slammed closed. Ironically, the widening emotional distance between the two of you actually degraded any empathy you had for your formerly cute little sister and made it easier to sexually objectify the little brat. By the time you’d rejected the world and begun working on an escape route to a fairer world where your cock could express itself, any familial restraint had been completely eroded to dust and replaced by pure sexual frustration and undue resentment.

What had begun as the occasional guilty, late night spank session whilst browsing her social media bikini pics on your phone followed by immediate post-nut guilt and self-loathing had progressed to a conscious decision to listen at your door for the sounds of the bathroom door opening so you could sneak harmless photos of her half-naked wet teen body walking down the hallway, fresh out the shower and wrapped in a damp towel whilst pretending to text. Eventually, the relentless injustice of being the stereotypical basement dwelling loser with a weak moral compass surrounded by hot unattainable women pushed your wank sessions to a new ****. Shortly before the Entity graced you with the promise of limitless deviancy, you had become comfortable with fantasising about fully dominating your little sister against her will, slapping her perfect little butt, twisting her cute little nipples, pushing her up against the wall and exploring her mouth with your tongue - and then grabbing her by the throat, pinning her down and putting her in her place by fucking the ever loving shit out of her. Usually whilst jackhammering your lubed up cock with a tight grip that you imagined was her broken in cervix, imagining her screams of pain turning into moans and incomprehensible babbling and drooling as you **** orgasm after involuntary orgasm out of her tiny body as you rearrange her feminine organs with your frustrated cock.

Yeah, you were just the best brother alright. Whatever, it was always just an idle dark fantasy, nothing you had ever entertained the idea of actually doing. I mean come on, you weren’t an actual psychopath incapable of distinguishing reality from fiction. As much as she might piss you off, Rosaline was still your little sister, and you really did love her, even if her teen bitch phase made it difficult to remember that sometimes. You simply enjoyed enhancing your jerk off sessions by harmlessly fantasising about forcibly stretching out her womb with your massive cock on occasion, that’s all.

Except… you were in a different timeline now. And the girl sitting to your left wasn’t Rose, was she? Not really. The real Rosaline was back at home in her room and wouldn’t remember any of this. Hell, none of this would really happen, not really. The Entity said as much, this was just for data collection. Just one possible unlikely timeline. The whole universe is offering everything and anything you want with zero consequences. The girl to your left might be a real person, a real version of Rose, but one without a future if this timeline never happens. So anything you do to her is fine, right? And if the universe saw fit to trap you between skimpily clad, porno versions of your sisters in a hot, sweaty car, with tits and legs on display, and a raging hard on that apparently only one of them had noticed, then what’s a guy to do but accommodate it? It's not like you have a choice anyway... right? If you don't act, you'll only have to at some other point in time. It's out of your hands.

You look your little sister up and down, openly perving on her exposed skin. Whilst her tits are on the small side, your eyes are drawn to her slender, cute tummy with a hint of toned abs, currently glistening in droplets of sweat. God, you could probably fit both hands around her waist if she sucked it in. It would be so easy to manhandle her.

She gives you the stink eye and mutters something about a fucking pervert under her breath before huffing and leaning in, yanking the water bottle out of your hand and jerking it away. She scoots over on her seat as far away as the cramped space will allow and smirks at you. You hadn't even decided which of your sisters you wanted to be nice to yet!

"Fucking loser. Think with your brain instead of your dick next time." She uncaps the water and starts to chug. Before you can react, Marie speaks up on your behalf.

"All you've done for the past two hours is bitch and whine and moan! David was kind enough to share the last bottle out of the goodness of his heart, but noooo. You just had to be a greedy little bitch like always, didn't you? You know what? Fuck you."

Marie unbuckles her seat belt and leans over you, crushing her pendulous tits against you in the process. She grabs the water bottle and squeezes it hard, forcing water down Rose's windpipe and all over her top. Her nipples poke little bumps in the wet cloth as the jolt of cold water seeping into her top and bikini freezes them. Rose starts hacking and coughing, spluttering droplets all over the place as she coughs up the forcefully inhaled water.

Her eyes watering, she looks over at Marie with hurt indignation on her face. Coughing into one hand, she frowns and slaps at the both of you. The sudden movement locks her seat belt, and she huffs as more air is **** out of her lungs. Her attempts at smacking the two of you thwarted, she lashes out with her legs. You grab her by the ankle as she attempts a kick to your groin and can't help but laugh at how feeble her attempts are. Come to think of it, didn't the Entity say something about you being unable to come to harm? You could just let your little sister have her tantrum without fear, but then again...

With your hand grasping her firmly by the ankle, you do have a clear view up her smooth, slender legs to her panties. Beyond even attempting to pretend not to stare, you wait for her to lash out with the other foot before grabbing that, too. Lifting her legs up, you pull them across your lap as she continues to struggle to unlock her belt. The latch is twisted up and pinned underneath her.

Keeping hold of one leg, you run your hand up her calf to the underside of her knee. Moving past the softest skin on earth, you lick your lips as you slide your hand up and grope her thigh.

"Holy shit, dude", Marie says. "You're my kind of freak!"

You feel your big sis's giant tits pressing against your back as she reaches around you to grab Rose's legs and help hold her in place.

"I've had about enough of this little brat, you finally gonna teach her a lesson? Great. Let me help." Her breath tickles your ear as she whispers conspiratorially. "We're gonna need to keep her quiet though, Clara's an oblivious cunt at the best of time, but even she'd notice her precious little angel screaming the house down."

Marie lowers the little plastic sunscreen on her side of the window, and you quickly follow her lead and do the same on Rose's. With the front passenger seat filled with camping gear, the only way somebody could see in is through the back or front windscreens, though you plan for all the action to be below head height so the only thing to worry about is your step-mom looking into the back seat. Not that you're particularly worried. If you get caught, it's some other version of you who'll have to deal with it.

Marie reaches under her step-sister and fidgets for a second as she unfastens the buckle acting as a makeshift harness, before grabbing her by one of her twin-tails and yanking her across your lap. Before Rose can yell, she finds the palm of her elder step-siblings hand firmly clasped over her mouth.

"Keep quiet, you little bitch. This is payback for all the time's we've had to put up with you," Marie hisses. "Keep quiet, or you'll just make it worse on yourse- AH! Fucking cunt just bit me!"

Marie jerks her hand away, sucking on the red semi-circle of bite marks around her thumb. You're about to replace her hand with your own, comfortable that Rose will be unable to repeat the trick, but Marie acts first.

"Right. That's it. I've had enough. You want to be a little bitch? You want something to drink? Want to bite me? I'll GIVE you something alright! **** on this, you little rat!"

Marie grabs Rose by the back of her head and twists her fist into her hair, yanking her head up at an uncomfortable looking angle. You stare on, your erection rubbing against the struggling girl's tummy as your sibling-in-crime hovers above the poor girl's head. With her neck craned back 90 degrees, Marie spits into Rose's mouth and grabbing her wrist, shoves her fingers back inside her step-sister's open maw. She leans in close, inches away from her face.

"Go ahead, bite me again. I fucking dare you. See what happens. I want you to do it. Give me the excuse. Fucking do it."

Rose just sobs, still writhing on your lap and failing miserably to fight off either of you. God, she's so weak. So fuckable.

"No? Didn't think so," Marie sneers, shoving her fingers deeper into Rose's mouth. You watch her throat pulsate as she gags on the intrusion.

She smiles and winks at you before whispering in your ear. "Enjoy your reward. You earned it, and the little slut deserves what's coming." Rose tries desperately to shake her head and mutter her objections through a mouthful of digits and drool, but Marie ignores her and gives you a big wet kiss on the side of your cheek. The last thing you see before focusing on the imminent blowjob is Rose's helpless, drooling and tear streaked little face looking up at you in a silent plea for help before being lowered down onto your throbbing erection.