Mark sat in front of the TV, controller in hand, ruining his Kill-Death ratio in his currently favorite shooter but not caring much. While the game was usually more than enough to grab and keep the thirteen-year-old's attention, right now he was just looking to kill time. Emboldened by the surprising success of Stacey's last brother-sitting job a few weeks ago, their parent's had gone away on a romantic weekend to some B&B just outside of town. The two had left the house holding hands, safe in the knowledge that when they come back they won't find one of their children covered in dirt, holding a shovel, and claiming their sibling had run off to join the circus. Mark tried not to think about what the two would be doing, focusing instead on the night ahead.
                As per the standing agreement, his sister was allowed to have her girlfriend over in lieu of payment, and the mousette was on her phone the moment she'd closed the door behind their mom and dad. His character got blasted as he remembered what had happened the last time Becca was over. Although there were aspects of the night that were still... confusing... to the young mouse, he vividly and fondly remembered being led into his sister's bedroom and allowed to join the two amorous teens.
                Well, truth be told, it wasn't 'Mark' that had joined them. But if wearing a dress and being called 'Marcy' is what it took to have a threesome with two sexy girls, he'd pay it in a heartbeat. His sister had acted like nothing had happened since that night, but Mark was hoping things would change once Becca arrived, since the whole thing was initially the hyena's plan.
                When the doorbell rang Mark had to stop himself from jumping up and running over to open it, deciding instead to try and play it cool. He figured he may have overdone it a bit, since the hyena-girl just gave him a quick 'Hi!' from the doorway, before his sister led her to the kitchen. The mouse's ear turned frantically, desperate to hear the two over the noise of the game, but with little success. He kept it up for a few agonizing minutes, and was on the verge of switching the console off and joining the two when they walked into the living room.
                "Mark, go to your room, Becca and I want to watch a movie." Stacey said, dashing the mouse's hopes for tonight in a single sentence.
                "B-But..." the boy stammered, desperately trying to recover from the blow.
"No buts! I've let you have the living room the whole day, now it's my turn."
Mark looked over desperately to Becca, but the hyena just gave him a shrug and a half-smile. His ears dropped as he switched the game off and went upstairs, tail dragging behind him. Every step made him more miserable than the last, but once he opened the door to his room his mood changed. Laid out on his bed was a familiar sundress, a butterfly barrette, a hairbrush and what on closer inspection turned out to be a pale-pink training bra.
The mouse's ears perked up when he realized that even though Mark's evening was busted, 'Marcy' might still have a fun night ahead of her. He practically jumped at the pile of feminine clothes, realizing that the two girls had managed to actually get him excited over wearing the stuff. And he was excited, to the point that his hands were shaking, which combined with a complete lack of experience didn't make putting the bra on any easier. After a while he finally managed to hook the straps behind him without dislocating a shoulder. Once the bra was on, he slipped the dress over himself and picked up the brush. He remembered the way his sister had combed his hair to the side, and found it was easier now that it had grown out a little more. Once he figured he'd done a good enough job he pinned it in place with the barrette and cautiously made his way out of his room.
Very quiet, but very promising sounds were coming from his sister's room, confirming Mark's theory that watching a movie was just a ploy to get him up to his room and changed. The light spilling into the hallway told him the door to Stacey's room was open, and Mark was just about to head for it when he spotted himself in the hallway's full-length mirror. He had to admit, he really look like a girl in this get-up, the slightly padded bra giving him a pair of mosquito-bite boobs and making him look like a young mousette just into puberty. If that's what it takes Mark thought as he padded closer to his sister's room, hoping his blush wasn't showing through his fur.
If it hadn't been earlier, it was definitely showing now, as the mouse was greeted to the sight of his sister's rump, or rather the parts of her rump not obscured by Becca's hands. The hyena girl was reclining on the bed with Stacey on all fours over her, bending down to kiss her while Becca fondled her pert ass. He stood in the doorway watching the two, until Becca spotted him out the corner of her eye.
"Told ya..." she said softly in Stacey's ear.
The mousette broke the kiss, a puzzled look on her face until Becca gestured behind her with her muzzle. When the mousette turned around and spotted her 'sister' standing in the doorway she practically leapt of her lover, eyes wide and a hand shooting to cover her mouth, failing to disguise her glee.
"Omigosh, you were so right about the bra! She looks just like a girl now!" Stacey squeed.
"C'mon in, Marcy! Don't be shy, we're all girls here..." Becca said, getting up from the bed and padding over to the newly-arrived 'girl'. Mark's mouth dropped open at the sight of the naked hyena as she slowly crossed the room, tail swishing and hips swinging with every step. When Becca bent over to tuck an errant lock behind one of his ears, her ripe young breasts swung mere inches from his face, reminding him why he puts up with this.
As she dazzled the young mousette with her cleavage, Becca couldn't help but notice Marcy's little 'clit' tenting her dress. She was pretty sure Stacey's newfound little sister would join them after the time they had last time, but it was always rewarding to have your suspicions confirmed. Holding the mousette's gaze, she slid the dress off one shoulder and then the other, letting the thin garment fall to the floor, revealing Marcy's young body to her hungry eyes.
Mark felt a shudder run through him as the dress slid off, leaving him almost entirely naked in front of the buxom hyena. He started to raise his hands to the bra, not sure if the girls would want him to take it off, and was relieved when Becca lowered them back to his sides. He was relieved, because although he was reasonably certain he could take it off, he doubted he could do it without making a spectacle of himself. Becca put an arm around his shoulder as she led him to Stacey's bed, the older mousette biting her lip and rubbing her slim thighs together at the sight of her little 'sister'. He felt like he was walking on air as two pair of soft feminine hands maneuvered him until he was lying down flat on his back, the two girls looking down at him with hungry eyes.
Stacey bent over her little sister, planting a deep kiss on the surprised mousette's lips. Despite her act earlier she was very much eager to spend some quality time with her sibling, as her moist lips could attest. After breaking the kiss she hopped into bed with the dazed Marcy, putting one knee on either side of her sister's head and showing her just how glad she was to see her.
"Remember what we taught you last time?" Stacey asked sweetly, her spread legs giving Marcy a wonderful view of her slippery young pussy. The younger mousette remembered her lesson, extending her tongue and running it across her sister's slit, ending with a flick over her little pleasure-button.
"Ooh, good girl!" Stacey cooed, lowering her hips a little so Marcy could really put that tongue to work.
Becca sat behind them, for the moment content to watch Stacey gently grind her sex against her sister's face, her pert ass flaring as she straddled the other mousette's head. It surprised her to see the usually quite subby girl take charge like that, but supposed the big sister in her recoiled from the thought of submitting to a younger sibling.
Speaking of which, Marcy would need some attention too. Knowing she couldn't see her, she began to plant little licks and kisses along the insides of Marcy's thighs, delighting in the way her young body twitched from every surprise touch. In fact, one part was twitching particularly hard, so the hyena decided to turn her attention to Marcy's little clit.
Spreading her legs to get better access she nudged her muzzle against Marcy's little pouch, taking in her scent as she blew little huffs of air over her privates. Unlike Stacey, Becca was attracted to males as well as females, as long as they knew their place. And not even Marcy's smooth little sack could change the image of her as a pliant young girl in the hyena's mind. Putting her hands on the insides of the mousette's thighs she ran her tongue over that little pouch and up the underside of his twitching clitty, feeling the mousette shudder as she gave the tip a little flick.
She continued giving Marcy long and agonizingly slow licks, her ears picking up her squeaks even though they were muffled by Stacey's cunny. She let one of her hands drift away from the mousette's thigh and rummaged around blindly until she felt her hand close over a small tube. The top popped open loud enough for everyone in the room to hear and she suppressed a giggle at the way Marcy's little pucker twitched at the sound.
Mark was now worming his tongue inside his sister's drooling pussy, lapping up her juices as he felt her little nub bump against his nose as she slid back and forth over his muzzle. Looking up, he met Stacey's lidded gaze as she let out little gasps and squeaks of approval of his work. His own noises as Becca licked his shaft were probably much the same, but thankfully drowned out by the slit his mouth was almost buried in. He couldn't help but notice how big his sister's petite breasts looked from this vantage point, the nipples capping them stiff and perky, another indicator she was enjoying riding his face.
A sudden pop broke his concentration, and he wasn't surprised when moments later he felt the touch of cold goo being smeared under his tail. It would seem Becca was getting tired of teasing him. He let out an 'Eep!' into Stacey's pussy as his own was slowly invaded, his pucker stretching around Becca's finger. His sister grabbed his hands and put them firmly against her young teats, clearly miffed that she no longer had his full attention. As he relaxed, allowing Becca to probe further inside him, the young mouse resumed licking his sister's quim, his hands gently groping those firm young breasts.
Becca was glad to see Marcy was relaxing without being told, noting that this was going even easier than last time, although the little mousette was still deliciously tight. She kept licking her by now dribbling shaft as she started to gently finger Marcy's little pussy. The tight pink opening was stretched around her digit as the hyena sent her fingertip questing inside, trying to once again find the right spot. She found it sooner than she thought, the rhythmic clenching alerting her to Marcy's impending orgasm. 
With an impish grin, she grabbed the mousette's twitching shaft and pointed it at her sister's back just before she shot her first rope of pearly-white cum. Stacey didn't seem to notice, or just didn't seem to care that Becca was using her little sister to paint her back, Marcy's girl-cock sending streaks of white splashing against her grey fur. Once he was done she gave his sensitive tip a little lick, smiling at the way he winced at the touch, and pulled her finger out her now slick little hole.
"Such an eager girl!" she almost purred, pondering how to mount the little minx. "Stacey, lift your arms a little..."
The older mousette obliged, not sure what Becca had in mind, but hoping it wouldn't involve her getting up and off of Marcy's muzzle. She actually had a tiny climax when she felt Marcy shoot her goo over her back, and was working herself up for a really big one. Becca took hold of the younger mousette's ankles and started to raise her legs up and then forward a bit. She hooked each one under Stacey's arms, the older sister getting the idea and holding Marcy's legs so that her tush was raised and presented to the horny hyena behind her.
Becca almost licked her chops at the sight of Marcy's little gray rump, and the slick pink ring now on full display. The opening twitched every now and again, and the hyena could almost feel her shaft throb in response, eager to stretch it out. She lowered her muzzle and began playfully nipping Marcy's cheeks, enjoying the way the girl tensed up when her teeth pinched her soft rump.
After she had teased the girl as much as either of them could take, she knelt in front of the offered derriere and spread her legs until her pseudo-cock was at just the right height to penetrate that tight little love-tunnel. Her eight-inch clit was hard and just waiting to burry itself inside the little mousette, but Becca took a few seconds to slather on some more lube, intending to give Marcy the ride of her young life.
Mark did his best to keep slurping his sister's snatch, although the older mousette seemed to be getting off just riding his muzzle. His hands were still on his sister's breasts, kneading the pert mounds and every now and again brushing against a stiff nipple, to Stacey's delight. He was aware of how exposed his rear-end must be, especially when Becca started to land little love bites all over his butt. Still, he couldn't deny that he was eager for her. His first time he'd been afraid, unsure if he could even take the hyena's rod, but now he found himself wishing she'd stop teasing him and just put it in.
Becca put her thumbs on either of Marcy's cheeks and spread them even wider, actually stretching his little pussy open slightly as she nudged the tip of her shaft against the slick entrance. She grinned as the mousette relaxed, allowing her to easily push the tip of her girl-cock inside that warm, tight little ass.
"Ooh, someone wants it bad! She's practically sucking me in..." the hyena teased as she slowly but steadily fed more of her shaft inside the prone mousette. It was an exaggeration, but not by much.
As she pushed further and further in, Becca had to bite her own lip as the sensation of Marcy's tight little butt threatened to push her over the edge before she'd even hilted inside him. The hyena loved pussy, but most of the time when she was fucking one, she had to stick a finger or two in her own snatch to really get off. But there was something about a nice, tight tail-hole that could make the hyena cream herself several times during one furious session. And Marcy's ass was the snuggest little hole she ever had the pleasure to bury her bone in.
She watched as inch after thick inch slid smoothly past that taut pucker, her hands on the mousette's hips, helping support his weight. She could feel slight tremors running through his body, his ring tightening around her every now and then, but never really clenching up. This wasn't like the last time, when the 'girl' had been all nerves and instinctive reactions. This time she was getting off on it when Becca had barely even started. It was nice to see she was so eager for her, although the hyena had to admit the nervous virgin thing had been really cute...
Mark was barely even licking his sister now, letting the mousette ride his face while he squeaked into her muff as his ass was slowly but surely claimed. He felt himself open up around Becca's rod, trying not to squirm as the hot, steely length pushed further inside him. There was no pain this time, and barely any discomfort as his body accepted the hyena's shaft. So lost was he in the sensation that he was almost startled when Becca's crotch bumped against his cheeks.
"Mmh, eight inches without so much as a peep! You know Marcy, if I didn't know better I'd swear you've been raising your tail for someone else..." Becca teased as she ground her hips against the mousette's rear, letting out a happy little murr as her wriggling shaft made Marcy's pucker squeeze around her. She was sure the girl was blushing somewhere under Stacey's gyrating crotch.
"Well, now that you're a big girl I can really give it to you, and not hold back like last time..." she said sweetly, pulling out almost all the way out of that grey rump before sliding her whole pseudo-cock back in to the hilt. The angle she was penetrating him at meant her tip had ploughed right into his little sweet-spot. Becca had to suppress a giggle when Marcy squeaked into her sister's cunny hard enough to make the older mousette squeak in turn, the ecstatic little sound traveling from one sibling to the other. She kept up her pace, fucking Marcy in long, loving strokes, curious to see if she could make them do it again. She'd definitely have fun trying...
Mark now felt himself assaulted on both ends, his sister grinding her slit across his soaked muzzle, her clit bumping against his nose on every stroke, while Becca sawed in and out of his ass, hitting that special spot every time she sheathed herself inside him. Still, he had no intention of asking his sister to get off, knowing the sort of noises that would be pouring out of his mouth if Stacey's cunny wasn't smooshing against it. He wasn't sure if it was the new position, or the fact he wasn't as nervous as last time, but the sensation of Becca's firm shaft pumping in and out of him felt even better now, and if his ass wasn't already served up to the humping hyena' he was sure he would have thrust it out.
Becca picked the pace up a little, feeling on the verge of the first of what would be many climaxes. She still kept her strokes long, enjoying the sight of her organ sliding in and out of Marcy's slick hole, and the messy smacking sounds her hips made when they slapped against her rear. The mousette's tail-hole clenched a little at the rougher treatment and the hyena bit her lip, barely slowing down as her girl-cock throbbed. She slid one hand between her legs just in time to catch a few squirts of her honey as her pussy gushed, lifting it up and drizzling a bit over Marcy's stretched pucker, already a slick mess from all the lube she'd worked into him earlier. Considering her efforts were already getting Marcy hard again, things would get a lot messier before the three of them were done.
"Hard again already? I must be better at this than I thought." Becca gloated as Marcy's little girl-cock flopped about with her every thrust.
"Ahh! Wait! I wanna..." Stacey gasped out and got off her 'sister', revealing the mousette's very surprised and very messy face.
Becca stood there, slightly less confused, holding Marcy's legs up while her sister did her best to settle down on the bed on shaky legs. A look at Stacey's face made her realize what the older mousette intended, and she slid out of Marcy, smiling a little as the prone 'girl' let out a needy little whine.
"Wh-why did we..." Mark trailed off, surprised that the action had stopped and that he now seemed to be the center of attention for the two girls in a somewhat different way.
"Well, Marcy... You know that I've never been attracted to boys, right?" Stacey asked her dazed sister who responded with a confused nod "The thing is, when you're 'Marcy' I find you really sexy. I mean, you're kinda like a girl with a little something extra. Sorta like Becca."
"Well, maybe a travel-sized version." Becca said smugly, giving Marcy's smaller shaft a prod to illustrate her point.
"What it boils down to is that, if you want, I'd like to have you, uhm, inside me..." Stacey said, looking bashful yet hopeful.
"Y-you mean in your...?" Mark asked, lowering his gaze to rest between his sister's legs. The older mousette's folds had felt pretty amazing wrapped around his tongue, and he was certainly eager to feel something like that on his shaft.
"Well, not my pussy. I didn't remember to get condoms, and I'm not on the pill since it's not like Becca can knock me up..."
"Not for lack of trying!" the hyena interjected. 
"Buuuut..." Stacey trailed off coyly. Mark looked from her face to Becca's, unsure if his sister was suggesting he desperately hoped she was.
"Butt!" Becca confirmed, grinning at the expression on Marcy's face.
"Y-yes!" Mark peeped out, his voice breaking from excitement. There were times to play it cool, and times to grab what was being offered. And considering what was on offer, he had no intention of playing it cool. Stacey seemed thrilled with his decision, although he imagined she couldn't have been very surprised by it. She bent down and planted a quick kiss on his lips, not minding the fact they were covered in her 'lip gloss'.
"Ok, now scoot over!" she said, almost rolling him out of bed.  She took a couple of cushions and placed them on top of each other near the middle before lying down on her back with her rear propped up on them. She put one hand behind each knee and pulled her legs out of the way, biting her lip as she served herself up for her little 'sister'. She felt giddy and a bit nervous, almost like she was losing her virginity all over again, which in a way she was. Even though it was smaller than Becca's clit and most of her toys, this would be the first actual penis she ever had inside her.
Kneeling between his sister's legs, Mark was saying goodbye to a virginity of his own. His eyes swept over Stacey's svelte body, from her perky teats, down her trim tummy and the by now messy crotch with that lovely pink slit nestled between two shapely legs. Inching further down he spotted her pink pucker and wondered what it will feel like being on the other end of butt-sex. A pat on his shoulder snapped him out of it as Becca pressed a by now familiar tube into his hand.
"Don't be stingy!" the hyena said with a smile, giving Marcy a pat on the butt to get her going.
Stacey took deep breaths as her little sister squeezed out some goo on a slim finger and lowered it between her legs. She gasped as she felt the cool slime get rubbed into her tail-hole before Marcy gently pushed her digit in, eyes wide as she watched her sister's ring stretch around it. She was still confused about feeling this way about someone she knew for a fact to be a male, but those feelings were melting away under her sister's loving, if inexperienced, touch.
"Now just slide that one finger in and out slowly for a minute or two. Then you very carefully slide another..." 
"No -ah!- I'm ready..." Stacey gasped, interrupting Becca's tutorial.
"How come? Whenever you let me under your tail I have to spend at least five minutes down there before you let me have any!"
"Well Marcy's sm... not as big as you..." Stacey replied, stopping herself from inadvertently causing a blow to the other mousette's ego. She couldn't risk it going down.
"Well, you heard the lady, Marcy..." she said, giving the younger mousette a light smack on her cheeks, slightly upset at this blatant display of nepotism.
Stacey would always remember the cute and slightly awkward way her little 'sister' had positioned herself, making her way up the mousette's body until her face was level with her breasts and that little shaft was prodding at her rear. Fortunately Becca stepped in and maneuvered Marcy's tip until it was nestled against her sister's shiny pucker. The mounting mousette gave an instinctive buck, burying the tip of her slim shaft between her sister's cheeks, both siblings gasping in unison at the sensation.
"Ah! Like that, Marcy. More..." Stacey panted as she urged her sister on. Any doubts she may have had about this went out the window, replaced by the urge to feel Marcy fill her, ride her. She wasn't sure if it was the fact that she was already maddeningly horny, or the fact that her sibling was smaller than Becca, but she wanted, needed her to give it to her harder. Fortunately Marcy didn't need much urging, her hips quickly settling in a vigorous rhythm, her little grey butt rising and falling as she humped her sister's tail-hole. She felt her bury her face in her neck and kissed the top of her head as the little mousette huffed and puffed into her fur.
Becca was kneeling behind the two, watching Marcy pump away at Stacey's pucker, listening to the cute sounds the mice were making. The two had crossed a very significant boundary, and she felt she owed them this intimate little moment together. But no more than a moment she thought, the sight of Marcy's still slick butt waving in front of her face being too tempting to resist.
Mark was glad that he'd already come once while Becca was fingering him, otherwise he was sure he wouldn't have lasted more than a few thrusts in Stacey's pert butt. The warmth, the tightness, the sounds his sister made every time he sheathed himself inside her, all threatened to overwhelm the young mouse as his world narrowed down to the sensation of Stacey's pucker wrapped around him and her slim body writhing under his. So when he suddenly felt a pair of hands palm his own cheeks, he almost jumped out of his skin. He turned his head slightly in time to see Becca position himself behind him, a grin on her face as she effortlessly slid her girl-cock back inside him. He fully expected her to continue pounding him when the hyena simply crossed her arms under her ample chest and stood there, buried almost to the hilt inside his rump.
"Don't mind me, lover, just go back to what you were doing..." she said in a sugary-sweet voice.
Mark didn't need to be told twice, and he did his best to pick up the pace he'd set before the hyena had penetrated him. This time, however, every time he pulled out of Stacey, he slid further back on Becca's shaft, only sliding off it when he thrust. He blushed as he realized he was fucking himself on Becca's girl-cock by humping Stacey. To make matters worse, the sensations were even more intense now, as both his shaft and his prostate were stimulated simultaneously. Still, he did his best to ride it out, hoping he could make his sister feel as good before he finished.
As far as Stacey was concerned, the sight of her sister taking Becca's shaft at the same time she rutted her tail-hole was a major turn-on, bringing the panting, moaning mousette even closer to what was threatening to be a mind-shattering orgasm. She kept one hand spreading her leg while the other squeezed between her and Marcy as she began to finger her sodden snatch. With her sister's shaft inside her, her love-box seemed even tighter, and she could feel the motion of the cocklet sawing in and out of her ass.
"Please, Marcy *ngh!* harder! I want... I want..." the mousette trailed off, her brain too frazzled to form a sentence.
"You heard the lady, Marcy, lets really give it to her!" Becca cooed as she lowered her front until she was supporting herself on her arms, her lush breasts pressed against Marcy's back as she gave her first, hard thrust.
Mark squeaked as the hyena's hips smacked against his sore butt, his sister letting out a matching sound as the thrust launched him into her as deep as he could go. He pulled out slightly, only for Becca to give another buck and once again push him all the way into his sister. A few more jabs and Becca had picked up a rhythm, literally pounding him into the squealing, moaning mousette. He could feel her stiff nipples pressed into the fur on his back, her crotch smacking against his ass as she fucked him in short, furious strokes, that steely shaft now barely leaving his ass. And all the while Stacey's insides squeezed around him, rubbing along the length of his young cock as it twitched inside her with every bump against his prostate.
It was all too much for the poor mouse to take and he soon felt his little sack tighten up as his young cock sent pulse after pulse of virile mouse cum deep inside his sister. He buried his face in her neck and clung tightly to her as he emptied himself inside her, every twitch of his shaft also tightening his pucker around the piece of hyena meat impaling him.
Once Becca had started railing Marcy, Stacey was a mess, moaning and mumbling incoherently as she rubbed her clit, needing just a little extra stimulation to set her off. When she felt her sister's little shaft twitch and start to pump her load inside her it pushed her over and the mousette let out a high-pitched whine as she came. That was the first time anyone had ever cum inside her, and in the throes of her climax Stacey was sure she could feel every hot, gooey spurt being shot deep inside her.
After Marcy had started cumming and her pucker started twitching like crazy around her, Becca had her own orgasm, grinding gently against the mousette's pert cheeks as she bred her sister's rump. Feeling finally sated, at least for the time being, she got off her and rolled over, laying on her side as she watched the two siblings pant as they clung to each other. Once she'd judged Stacey had gotten her breath back, she put her hand on her chin and turned her head until she was facing her. She then planted a soft but deep kiss on her muzzle, a loving gesture and a little reminder of whose girl she was.
Not that she minded Marcy joining in. And they had a lot more fun ahead of them, although apparently not just now, as Marcy seemed to be fighting a losing battle trying to keep her eyelids open. In the meantime, Becca continued to kiss Stacey as the mousette cradled her sister's head against her breasts as the content 'girl' drifted off to sleep.