The night crept outside; its shadowy veil sharply punctured at regular intervals by the lights on the street. Moonlight broke at the glass window and faintly showered the room with its sheen. The place, however, remained mostly pitch-dark. Two beds occupied most of it, and two girls were inside. A couple of bags lay sprawled on the floor next to the big wardrobe, and two nightstands adorned the side of each bed.
Sidney and Emma, sisters, eighteen and twenty-one, had been reunited by Christmas tradition. The family had come together, as per yearly custom, to celebrate the merriest time of the year. The parents slept heavily at the end of the hall, in the biggest of the rooms. One door before that a single bed remained unoccupied while the elder brother was out partying. And finally, to the left, the girls' bedroom sheltered the two siblings from the cold outside.
It was around 2am when she felt it; it was the younger of the two, unable to sleep, who this time felt that tingling, that urge. She had been thinking about it all week, waiting, dreaming, and now had appetite for it... her sister's ass. Christmas night would mark two years since the first accident. The girls had discovered a new taste of fun and pleasure, and it had changed them forever.
Lithely, she got up in silence and started moving in the shadows, her slender teenage shape waving a slight inverted S shape on the floor when she crossed the window in the middle of the room, prowling towards her sister's bed. She stopped next to her bag and picked something up. Despite the darkness she could make out the contour of the body below the sheets, and there it was, her prey; propping the silken cloth in resemblance to a hill was her sister's big, round butt, and in between those firm cheeks, her objective. Praying for no creak from the wooden floor, she advanced until she reached the other bed, and slowly climbed up the backside and got onto her knees. Methodically, the lustful girl began pulling back the blanket, and then the sheets. There it was, just like her memories pictured it. A grin sparkled in the dark.
Sidney was already wet with excitement, but, composed, she examined her prize before taking it. Her sister had always been fit, and her body reflected it. The curves were chiseled into her petite body like a statue, and it all flowed down onto the last and best one, her ass. Big for her body, meaty, it puzzled Sidney how a thing so soft and pillowy could go hard as it would when her sister flexed to show off.
Her hand moved on its own. She started caressing the skin, her insides shaking with excitement for what was about to come. Soon both her hands were on her sister's flesh, and after putting the panties to one side, the desire was just too strong; she pulled apart the cheeks to reveal a hint of her sisters pussy and above, puckered, tight, and delicious, her asshole.
"W-what the fuck are you doing?!" Yelped Emma drowsily who had just woken up to a creature on top of her, spreading her ass.
Her sister retorted with a smirk. "You know exactly what I'm doing, sis." and, without hesitation, she stuck her middle finger into the unsuspecting hole.
Emma's eyes shot open. A weird mixture of pain and pleasure invaded her behind. She squirmed and struggled to turn around, but her sister reacted quickly, turning a hundred and eighty degrees and sitting on her back.
"Stop, it's not right, we promised we wouldn't do this again!" the older snapped, yet in a soft voice, so as to not wake anyone up, or unconvinced of what she was saying.
"Oh I am such a naughty girl; promises don't work with me, Emma. You should know that by now." Her sister responded while starting to move her finger back and forth.
A light moan betrayed Emma's feelings.
"So, no more, huh? You totally don't want this, is that so?"
She was already beyond confused. She definitely did not want this. They were sisters, it was wrong! And it was her butt! They shouldn't be doing this. The other times had been mistakes, they were behind them. And they, they had promised not to do it again . . . but her body, what was this feeling, why was it electrifying her so much? Her mind raced for answers, but she found nothing, nothing but an overwhelming feeling that roared over everything else: pleasure.
Sidney did not waste time, she had thought this through already, and she was going through the steps. A second finger jostled for space inside her sister's ass, while her other hand grabbed tightly one of the butt cheeks, fingernails digging in like little hooks.
"P-please stop" Emma uttered in a defeated voice. A moan followed, flagging the statement as a lie. "It's disgusting, you shouldn't do this!"
"Disgusting?" The girl on top looked perplexed. The fingers stopped and came out. "Well then how about this" she said while lowering her head.
Emma broke when her sister's tongue went in. She couldn't take it anymore. The feeling was intoxicating, it was stronger than her, she loved being tongue-fucked. She had discovered this soft-spot last year, when her sister had become suddenly brave and gone beyond anything previous. The promise vanished and no more resistance was faked. Taboo be damned, Emma covered her mouth to stop moans from loudly emerging, and delighted in her sister's love.
It seemed as if Sidney had practiced this during their time away; she appeared to be an expert at it. It started with a plunge of the tongue, and after some quick movements inside she took it out and started mixing in kisses with thrusts. Her hands worked the cheeks as dough, spreading and fondling them in different ways while her mouth focused in the center. After a while she went for another dive and kept it inside, twisting, twirling, straightening, receding, curling and finally going as deep as she could. She then took it out and started working with the tip, licking in shifting patterns and movements, rimming the now throbbing asshole and its surroundings, going up and down the slopes of her bones. Occasionally she would detach, go down to her pussy and work the way up, kissing, sucking, and licking in a march of wetness, blaze, and pleasure.
An eternity seemed to pass in Emma's brain, but the trance was shattered when her sister spoke. "It's becoming loose, you're ready for it".
Sidney reached for the end of the bed and grabbed it, a 7 by 5 inch dildo. "Now the real fun begins, sis". She said while adjusting the tip of the rubber cock to her sibling's forbidden hole.
A zap of shock quickly came and went through the elder's head, her arousal now dictating her thoughts. She wanted it. "Put it in, you bitch, look at what you made of me". Her pussy was melting, and her hole pulsating with anticipation.
Sidney started pressing it in, Emma's ass gradually opening to allow this intruder. She was patient, slowly pushing and pulling back, allowing the sphincter to adjust to the size. Finally it opened, and the head going in was crowned by a long repressed moan from the eldest, and a lewd, self-satisfied face from the youngest. Once it was in Sidney did not wait to push, and further it went; Emma's anatomy adjusting to the foreign object in her butt.
"Oh my god, I love it, fuck me Sid, fuck me please." Begged Emma
And so her sister did.
Her lust unquenched, Sidney took her hand beneath her clothes and in between her legs while her other arm started to pound her sister's ass. She fingered herself to the muffled moans of her sister being fucked by her toy, her wetness now passing through her clothes onto her sister's back.
She was also thorough with this instance. Taking advice from the internet, she tried to imitate the movements she had seen and read about. She went in intervals and different tempos, made variations in the depth of the thrusts, and as a plus, rotated the toy with her wrist, to which her sister squeaked and jolted.
"You love this, don't you, you little slut." teased Sidney. "You love to have your ass pounded. And you dared to bring that silly little promise to the table, look at you now!"
Emma couldn't respond. Her brain was numb. Sensations pulsing from her ass rippled throughout her entire body. She was being brutally fucked in her ass, in the middle of the night, with her parents down the hall, by her own sister . . . and she relished every second of it. It was sick, and the taboo only made it better for her. She quickly took her hands to her pussy and started working it. "Y-Yes, I love it, I'm a naughty slut." she finally conceded
