Your Sister uses her pussy to test your willpower

Ruby eventually takes a moment to use the bathroom to properly wash the remnants of cum off her face, which you feel a brief pang of disappointment upon hearing before shaking that thought out of your mind. You also decide to take a moment to get yourself clean, opting to use the main bathroom while Ruby uses the en-suite. The entire time you can't help but think back to the sweet memories of what just happened, which unfortunately means that by the time you're done showering your cock is already starting to stir. So when you walk back into your room and see Ruby lying naked on her front ass towards you, your cock is rock hard once again.

Your older Sister glances back at you at the sound of the door, spying the prominent bulge in the towel wrapped around your body she lets out a soft sensual laugh. "Damn Sis, you know how to make a girl feel wanted," Ruby jokes with a big smile.

"Sorry," You apologise nervously, trying in vain to somehow tuck your erection to be less prominent, but only making it stand out more in the process.

"Nah, it's my bad, I kinda hoped I'd have that effect on you," Ruby admits with a big grin.

"You did?" You reply hesitantly.

"Yeah, firstly because it's a nice boost to my confidence that I still got it," Ruby says with a grin, getting up and turning around to face you.

"But, I'm your Sister," You reply hesitantly. "Isn't that weird to you?" You add nervously.

"Maybe at first, but honestly it's kinda a turn-on," Ruby replies with a nervous smile of her own. "Sort of the taboo nature and how wrong it is makes it exciting," Ruby adds with a smile.

"I guess," You reply, still not quite feeling comfortable with the situation.

"Secondly, I need that big bad Cock nice and hard for the next test, to help you build up that confidence so you can enjoy that huge gift swinging between your legs," Ruby says in a confident tone. "Now, ditch the towel and lie down on your back next to me," Ruby continues, patting the bed.

Nervous, excited, confused, aroused and all manner of feelings in between rush through your mind as you undo the towel and let it fall to the floor, your erection springing free and bobbing enticingly before your Older Sister's bright blue eyes. You go to take a step towards the bed before you suddenly stop and turn back to the door and lock it. On some level, you were already resigning yourself to the fact that things would once more get beyond your control.

"Good thinking, wouldn't want Mom or the twins to accidentally come back at just the worst moment," Ruby says with a smile, her eyes staring fixedly at your big thick length and the way it bobs with each of your steps.

You give your big Sister a half-smile, your eyes quickly taking in your Big Sister's naked splendour, her large DD cups, the soft curves of her enticing body, and the subtle almost imperceptible glistening of her pussy between her crossed legs. You take a deep breath through your nose, catching a faint hint of arousal in the air, although it was hard to tell if it was Ruby's or your own.

You slowly mount the bed and shuffle closer to your Sister, feeling a slight urge in the back of your mind telling you to pounce on your Older Sister and ravage her as you both want. You push the invasive thought away, the fact you do so with such ease filling you with a brief sense of confidence that this insane plan of Ruby's might be working. Although that newfound confidence soon melts away as, no sooner as you lie down on your back, Ruby straddles you.

You let out a gasp of pleasure and surprise as you for the briefest moment feel the wet warmth of your Sister's labia brush against your cock. "Ooops sorry, got a little too close there," Ruby says with a giggle as she steadies herself. "Sure, you didn't mind too much," Ruby adds with a teasing tone. "I know this big beast didn't" Ruby concludes motioning down to your thick shaft which twitches and oozes a small amount of precum onto your flat stomach.

"Just a little surprised is all," You admit, trying to steady your breathing.

"Good, don't want you getting too excited and popping off again before we can get into the second test," Ruby replies with a sultry tone.

"What is the second test," You ask nervously.

"Well I'd say it'll be a test of your willpower, but there's a physical element to it too," Ruby replies with a wry smile on her soft full lips followed by a soft sensual laugh which sends a shiver down your spine.

"What will I be doing?" You ask hesitantly.

"You, my sweet little Sister, don't need to do a thing," Ruby begins as she begins to adjust her position once more, lowering her hot dripping lips onto your cock, trapping it between her labia and your body. "Just keep yourself from moving, no matter how good it feels," Ruby whispers in a soft seductive tone.

You swallow hard, as your mind begins to fill in the many possibilities of what would soon be happening. But before any doubts or fears can set in, your train of thought is derailed as your Big Sister begins to slowly grind herself against your thick throbbing shaft. Ruby's juices quickly coat your rock-hard cock as she slides herself up and then down the shaft, the sweet heat of her pussy washing over your shaft, causing it to twitch and drip precum onto your body.

"That's it, just lie back and enjoy," Ruby purrs, continuing to grind her slippery sex against you, precum continually oozing from your tip. Your Sister spies the expanding pool of your precum, and casually runs her finger through it, bringing her sticky digit up to her lips before sensually sucking it clean. "Mmmm pretty tasty, I wonder if your cum will taste as good," Ruby adds with a sexy little giggle.

You lie back, unsure of where to look, focusing on your Big Sister's naked form as she writhes against you feels like it'll only end in disaster, yet looking away feels wrong. So instead you close your eyes, and try and focus on the scintillating sensation of your Sister's sex sliding along your increasingly slippery shaft.

"Alright, that's enough of a warm-up," Ruby says after what was probably only a couple of minutes, but to you felt like several wonderful hours. "Time to play a little game, that gets a lot of girls into trouble," Ruby adds with a sense of glee.

You finally open your eyes, when you feel the weight of your Sister's body lift off of you, although you soon wish you had kept them shut, as you watch in awe as Ruby holds herself above you, your shaft pointing right up towards her. With a devilish grin, Ruby reaches down and takes a firm grasp of your cock, and angles it to the entrance of her sweet lower lips. You bite down on your bottom lips when you feel the swollen head of your cock brush against your Sister's pussy, almost drawing blood with how hard you bite when your tip pop between your Sister's lips.

"Just the tip," Ruby says through a moan of pleasure.

Your fingers claw into the sheets beneath you, your mind reeling with wave after wave of excitement and pleasure. The sweet embrace of your Big Sister's pussy around the bulbous tip of your shaft. The very same Sister, who was the subject of the first taboo dreams all those years ago and who featured in many a depraved fantasy you tried to push away into the deep dark recesses of your mind. Still despite your very vivid and active imagination, never once did you picture yourself in this position. Your fantasies always featured you taking the lead, or being a mutual experiment, never did you picture Ruby taking control like this.

You lie back, trying your best to not move, to resist the urges in your mind, pleading with you to either thrust upwards and into your Sister, or to simply grab her by the hips and pull her down onto you. You can feel that bestial hunger, you felt with your half Sister, yet you find yourself able to ignore it. You couldn't tell if it was not wanting to let your Big Sister down by failing her tests which is giving you the willpower, or perhaps without Mira manipulating your mind it wasn't as strong, or some combination of the two. In either case, you simply take your frustrations out on the sheet beneath you, while Ruby begins to lift herself up and down onto your swollen tip.

"Mmmm, even the tip feels so wonderful," Ruby groans, resting her hands on your chest. "What do you think, Amy?" Ruby adds with a giggle, which vibrates through her body and into yours through your swollen shaft. "How does, Your Big Sister's pussy feel?" She asks in a teasing tone.

"Incredible," You gasp.

"Does it feel better, knowing how closely related we are?" Ruby begins to ask with a sexy giggle. "Not a cousin, not an aunt, not even a half-Sister," She continues, the closest relative you could fuck," Ruby adds. "Same Mother," She groans, "Same Father," She continues as genetically close as we could get without being twins," She says with a wicked laugh. "And I bet that fact excites you, doesn't it Little Sis?" Ruby concludes.

"Yes," you hiss unable to even attempt to hide your feelings, your toes curling as Ruby lowers herself a little further this time, taking the full first inch of your cock inside her juicy pussy.

"Ooops that was a little bit more than just the tip," Ruby giggles, lifting herself back up causing you to let out a soft whimper.

"Careful," You gasp, hands trembling as you continue to defy the primitive urges screaming at you, ' shared genetics be damned breed this teasing bitch'

"My bad," Ruby says in a sexy whisper. "You're just doing so well at this test, I felt like one of us needed to be naughty," Ruby adds, lowering herself back down, taking the first inch and going a tiny bit further this time.

"Ruby," You plead, softly, while you feel your Sister's juices dripping down your shaft.

"It's ok Sis, it's still mostly just the tip," Ruby replies, with a mischievous giggle.

At this stage, you know that it wouldn't be long, that one way or another you'll soon be fucking your Big Sexy Sister. The only question would be who would make the first move.