It was another rainy Saturday at Beacon Academy.
While most students were tucked away in their dorms, some had dared to brave the weather and try to make the most of their weekend, such as the leader of team RWBY, Ruby Rose. Others, such as Weiss Schnee and Blake Belladonna, were in the library, studying for upcoming exams. And lastly, some were in their dorms, but instead of relaxing they were desperately trying to complete projects for the following Monday which they had put on hold for too long. Yang Xiao Long belonged to this group.
The blonde huntress was sat at the desk by her room's door, scribbling down answers to topics she was sure had never been brought up in lessons before. Next to her lay a pile of unfinished papers that she'd all but given up on completing in time. Unfortunately, since they were in their third year at Beacon, it was unlikely that she'd simply get away with a slap on the wrist this time. She'd most likely have to resit this year, while the rest of her team continued onwards and upwards.
On the cusp of pulling her hair out, she finished her last barely coherent paragraph and dropped her dulled pencil. She then slumped back in her chair and sighed, looking around the room.
"Hmm, I don't suppose Weiss has left her homework anywhere…" Yang thought to herself, eyeing the heiress' schoolbag.
"Nah, she's probably got it locked up somewhere if she hasn't handed it in early. Maybe Blake? Or…"
Her plans of plagiarism trailed off as her gaze fixed on Ruby's bed; or more specifically what was on it. Her half sister's combat uniform was spread out neatly, having just been ironed. The red-haired girl was a complete mess with everything in her life except two things: her weapon and her cloak.
Not wanting to so much as catch a glimpse of the pile of work she should be doing, Yang got up and walked meekly over to Ruby's clothes and gently pulled them down.
"Rubyyy~" she murmured aloud, burying her nose into the corset, and savouring the smell. Fittingly, it smelled of the rose-scented washing powder the team leader liked using, along with a hint of her shampoo and perfume.
With a quick glance back at the dorm door, Yang slowly pulled her pyjama shorts down to expose her semi-hard cock and press it against the delicate fabric. She shuddered slightly at the touch, having not done something like this in a while. She wrapped her penis in the skirt fabric and began jerking off with it, her sniffing becoming faster and faster. She staggered down onto Weiss' bed as she neared climax. As she let out a few squeaks and moans, she came up into Ruby's clothes, wrinkling the otherwise pristine fabric and ruining the lovely smell.
Before she could slump back and savour the wonderfully relaxed state she was in, she heard running in the corridor that could only be coming from one person. With her heart kicking into overdrive, she jumped up and pulled her shorts back up, but didn't have enough time to fully toss the clothes back up on the top bed before the door violently swung open, crashing into the wall, and adding to an increasingly large dent caused by the doorknob.
"Hiiiiiiiiii Yaaaaaaaaaaang!" a squeaky voice exclaimed. Ruby was soaking wet, having just gotten back from town. A few dozen rose petals billowed out from behind her as her Semblance deactivated, and promptly disappeared before even touching the floor. She was wearing her school uniform since everything else other than her combat gear was too dirty.
"O-oh, hey Rubes! You weren't out long!" Yang stammered back, walking 'casually' back to the desk.
"Well, I mean, have you looked out the window? It's waaay too bad for anything fun. But I did manage to get some doughnuts from that baker you recommended! Got 'em right here!" she bragged, holding up a damp brown bag with the baker's logo on it. It looked full to the point of bursting, and the smell was maddening for someone like Yang who was trying to work on her diet.
Ruby walked over to her bed and jumped up onto it, with the rope audibly creaking at the sudden weight.
"Huh? Why does it smell weird…" Ruby murmured to herself, sniffing around. Thankfully for Yang she didn't find out where it was coming from.
Yang had sat back down but turned her chair to get a better view of Ruby. She was lying down with her back to the rest of the room, gobbling down the jam-filled treats she'd brought back and watching videos on her scroll. Such an angle gave Yang a great view of her half-sister's ass.
She'd never admitted it to anyone, but the older huntress had had a crush on Ruby for a while, at least since they'd arrived at beacon. While at first there was a romantic element to it, since then it had broken down into nothing but lustful desire, and this was entirely down to how Ruby had changed over the years.
Growing up, Ruby was one of those kids that could eat as much as she wanted and never gain even the slightest bit of weight, much to the jealousy of everyone else, Yang included. Some kids joked around that it was her 'second Semblance'. However, time had struck that theory down.
At home, Ruby at least had a father that would keep her diet somewhat in check, with her being forced to eat vegetables here and there. Now she had her own money and no supervision. She'd scoff down sweets and pastries in her free time and pick only the unhealthiest of options at Beacon's provided lunches. Beacon had done little more than hint at her that her eating habits were unideal, with lines like "a good diet is just as important as a good training schedule, if not more so". They didn't want to offend one of their most noteworthy pupils, after all.
What's more, while with Yang any extra weight would typically go to her bust, with Ruby it was almost entirely her lower body, specifically her legs and butt. This is when Yang started to take extra notice and went from trying to work up the courage to express her feelings to trying to catch as many glimpses of Ruby's ass as possible. And it wasn't like Yang was helping with Ruby's diet situation either, quite the contrary. She'd often recommend the fattest of pastry shops and would bring home plenty of pizza and burgers for her little sister to scoff down.
Recently, the situation had gotten much worse for the team leader. Her physical performance was dropping drastically, and she'd nearly run out of clothes that would fit her. In fact, her uniform skirt barely covered anything (something the rest of the student body had noticed) and she'd even stopped wearing the tights of her combat uniform.
Still, despite all of this evidence she was in complete denial, chocking her ill-fitting clothes up to her 'growing' or 'getting stronger'. No one wanted to be the one to tell her how she really looked; even Weiss had kept her mouth shut which was quite the surprise.
For the next five minutes Yang simply looked up at her soaking wet sister, noticing even the slightest jiggle in her thighs as she shifted positions. So far, she'd been content with simply staring, whether that be catching glimpses as Ruby walked ahead of her up stairways or appreciating how little the dorm towels covered whenever she stepped out of the shower. But lately she'd wanted more. By accident at one point Ruby had sat on Yang's face when she went to sit on Blake's bed, not noticing Yang was lying down on it. She'd masturbated to that moment at least once a day for a week after that, and she couldn't stand the thought that she'd never get to feel it again.
Regardless of whether or not it ruined their relationship, she had to feel it again. It wouldn't exactly matter if she got kicked out of Beacon for harassment, since she was already failing, right?
"H-hey Rubes? Can you help me out with this work? I'm kinda stuck" the pervy blonde spluttered out, grabbing a random sheet of paper off the pile, and plonking it down in front of her.
Ruby spun around and grinned cheekily.
"Oh, my dearest sister Yang. Needing help from li'l old Ruby, are we?" she teased, leaping down from the bed. Yang noticed how this sent ripples up her thighs, making her blush.
"Heh, yeah~ It's uh, this one. The whole thing petty much" Yang responded, pointing the premise that seemed the most complex.
She pushed her seat back to make room for Ruby, who leaned down to get a better look at the paper. Small droplets of water ran down her hair and landed on the desk. As this happened Yang pretended to drop her pen, slowly getting off her chair and kneeling down. And from this point she got the best view she ever could've hoped for.
Ruby's panties had all but been absorbed, thanks to her unbelievably massive ass cheeks. They were pale and spotless, except for a few hints of cellulite towards her upper thighs. It emanated a warmth that drew Yang in closer. Whenever Ruby shifted weight over to one leg or began writing her cheeks and thighs would wobble slightly, kicking off raindrops as well.
While Ruby was explaining away, Yang was having an internal fight with herself. She wanted to move her face forward, but something was keeping her from doing so. Her heart was racing, her mouth was dry and she was shaking all over.
"Aaaand that's what that one means! You with me so far? Yang…?" Ruby had turned around to see her older sister kneeling down behind her with wide, glazed over eyes.
"Y-yep! So far s-so good!" Yang stuttered out, sitting back up and gesturing to the pen she picked up.
Ruby gave her a quizzical look but then went back to the paper, and almost immediately Yang was on her knees again, her cock pressing against her shorts.
She knew that to go through with this she had to get caught, so this time she gave herself no excuse as to why she was on the floor, and there was no ambiguity as to where she was looking. It felt like minutes had gone by staring up at Ruby's ass, but it was likely only a few seconds when the redhead turned around again.
"This also explains the next premise. Did that help? Uhhh, Yang?" Ruby had turned around to the exact same scene, except this time Yang didn't respond. She just kept staring.
"Y-Yang? What're you doing?"
"N-nothing, just…"
She got closer.
"You just have such a beautiful gigantic ass~"
Both huntresses fell silent as they tried processing what had just been said, with the rain falling against the window being the only noise. Ruby nervously pulled her skirt down to hide the object of her sister's fixation.
Yang felt like she'd just stepped into one of her imaginations, only she was shaking a lot more than she'd expected.
"W-what? It's not gigantic, you told me so yesterday. Why would you say tha-?"
Before Ruby could finish her sentence, Yang finally lunged forward, lifting up the skimpy skirt and burying her head in her ass. This was it, there was no going back now. Any inhibitions she'd once had were gone. She grabbed at the flustered girl's ass and motorboated it, smothering her face in it even more. It had a funny smell she'd been expecting, but also that familiar rose perfume that only amplified her lust. Her ass was warm and soft to the touch.
"AAH! YANG?! WHAT'RE YOU DOING?! GROSS GROSS GROSS GROSS! WHY'RE YOU DOING THAT!"
Yang wrapped her strong, muscular arms around Ruby's waist and pressed her cheek up against Ruby's left butt cheek to speak.
"Sorry Ruby. You just have such a fat ass, I-I couldn't resist. It's just so big, y-your skirts are so short, you eat like a pig, I..I"
She was mindlessly stuttering out everything she'd ever wanted to say to Ruby. If this situation ever happened, she'd planned to go on a long speech about how fat her sister's butt had become, but she simply couldn't bring herself to. Her mind was racing too much to be able to put together coherent sentences.
"I-it's not fat! Why do people keep saying that?! Nothing's changed, you told me so! let me GO!" She screamed, pushing helplessly against Yang's grip. After a few more seconds Yang let go of her waist, but quickly grabbed onto her shoulders as she stood up.
"Yang, that was way too weird! Why would you do something like that? You're my sister! I'm gonna have to tell someo-MMPH!"
Ignoring her complaints, Yang had pulled Ruby into an intense smooch. Ruby's full lips were as soft and delicious as her ass. Yang kept her eyes open to savour the wide silver eyes before her. The older huntress intentionally moaned loudly and made slurping noises to get as much out of this kiss as she could. As Ruby came to her senses and tried pushing away, Yang clumsily walked the two of them over to Weiss' bed and collapsed onto it, with Yang on top. She felt Ruby's thighs squish to twice their size as they were pressed up against the bed, causing her thigh high socks to tear a little bit. After another two minutes of one-sidedly passionate snogging Yang pulled back, leaving several trails of saliva still connected to the scared redhead's face. It was a site Yang had fantasized about almost every night, and now it was happening.
"W-when will you let me go…" Ruby asked shakily, her whole-body trembling. Yang's body was trembling too, but for different reasons.
"I'm sorry Ruby, I can't. I've *kiss* wanted this *kiss* for sooo long." She replied breathily, stopping to sneak in surprise kisses after every few words.
After she was done drenching Ruby's face in saliva she sat up, kneeling over Ruby's waist. From there, she pulled down her shorts to let her fat, precum stained cock loose. The look of surprise and dread on Ruby's face was like art to Yang.
"You've been eating so much, getting fatter and fatter. And you still walk around in those tiny skirts like nothing's changed. You're such a dumb, fat bimbo Ruby. You made me do this~" Yang said, taking pleasure in humiliating Ruby.
She spun Ruby around so her jiggling, hickey covered ass was facing her, and she sandwiched her twitching dick in between the massive cheeks. They were so soft the Yang had to use quite a bit of strength when pressing them together in order to feel them.
"N-no! Don't! Not there!" Ruby begged in a shaky voice.
"No, don't worry Rubes… I wouldn't do that" Yang responded earnestly, beginning to slowly thrust her dick up and down.
"I doubt it'd even reach through these giant cheeks! I'm just gonna do this…"
She pressed her nose into Ruby's hair as she began hotdogging, with plenty of precum already staining Ruby's lower back. This only went on for five minutes before Yang was on the brink. Ruby's whimpers grew louder as she realized what was happening.
The bed was rocking violently and making so much noise that anyone who walked by the dorm would immediately know what was going down.
"G-god! I'm cumming Ruby! I'm cumming into your fat ass! Take it you fat cum dumpster! You're miiiiiine~!"
As she moaned the loudest she'd ever moaned, Yang's back arched and her eyes shut tightly as cum shot out across Ruby's back, some of it even getting in her hair. The whimpering only made the cumming last for longer. It was a sense of ecstasy Yang had never even known was possible. It was better than all her dreams, even the lucid ones. Once the climax finally subsided, she spread apart Ruby's ass cheeks to look at her work. Surprisingly, there was no cum in between them, as most had shot out up her back. She rested her head on Ruby's ass cheeks once more and yawned.
"Aaaah, that was nice, sis! We should do this again sometime!" the satisfied brawler exclaimed, regaining some of her typical confidence now that she was satisfied.
Ruby let out a small sniffle in response as Yang drifted off.
"Best. Saturday. Ever."