Ruby Rose, Her New Cock, and an Ero System (A LitRPG RWBY AU)

3. Slide

A cave system was a pretty common environment for a Rift to manifest as. Technically, anything could show up inside a Rift, but it was far more likely for Grimm to reside in dark, underground places than anywhere else. So when it came to that aspect of her and Yang's first-time Rift, they were treading expected ground. Which Ruby appreciated. She could use some normalcy.

About as soon as she had that thought, everything went off the rails again.

One second they were creeping down a cave tunnel, Ruby trailing just behind Yang, and the next, the stone floor beneath them had folded downward, and they were falling. Too fast even to scream in surprise.

The air-whistling descent lasted a quarter second before Ruby hit a slope, and then they were sliding. A slick, thick, slimy liquid coated the stone surface, and while Ruby—and Yang too, in her peripheral—tried to turn around, orient, and get a grip on a rock outcropping or similar, they didn't stand a chance. Not only was it a steep slope, perfectly smooth, but it was lubricated too. With…something? She had no clue what.

Down they slid, tumbling left and right, spinning, and thoroughly covering themselves in the slimy fluid as they struggled to orient. Barely seconds passed before Ruby was drenched in the stuff, her entire naked body coated in a thin layer of lubricant. They accelerated by the second, picking up enough speed Ruby lost track of herself and her surroundings, aura-enhanced senses or not.

Then, abruptly, the trip came to an end. The tunnel had been funneling them downward. Either by the slide's design or by coincidence, both she and Yang arrived at the same time, feet pointed downward—

—and slammed into a thin hole at the bottom.

With her aura active, it didn't hurt exactly, but they'd been going fast. They were shoved into the skinny pit, compacting all the way down in a tangle of slippery limbs, until their feet hit the ground.

And then it was over.

She and Yang were left standing there, in a thin cylindrical stone hole not remotely big enough to fit the two of them. Claustrophobia would've attacked her, but there was an open hole above their heads, and they were aura-empowered huntresses-in-training. They would be able to get out. It would just be a bit awkward, crammed-in and lubricated like they were.

Something other than escaping occupied her attention though.

Yang.

Their closeness. As in, they were pushed together so tightly she didn't think there was an inch of their skin that could be touching, that wasn't. Ruby took mental stock of their positioning. They were both standing upright, facing each other. Yang's breasts were shoved right atop Ruby's, with her big sister being several inches taller. Their stomachs were flush. Ruby's thigh, she was pretty sure, was between her sister's legs. And likewise, Yang's was between her own.

All of that would have been flustering enough.

But of course, a particular body part had been added to the mix, squishing against her sister, and that was a hundred times more compromising.

Oh no, Ruby thought. Stay down. Don't you dare.

"The hell? What is this?" Yang asked, her shock over the extremely unexpected descent wearing off. She began to wiggle, trying to dislodge herself from their tight confines. "And what's this shit all over us? What was that?"

However it had happened, Ruby's cock had ended up between their stomachs, standing upright—but at least soft. With Yang moving around? Wiggling her bumpy, slippery abs against Ruby's sensitive cock? Shaking her breasts in her face, brushing nipples across her, and tickling her own as well?

Ruby's cock sprung up at record speed.

Yang froze.

The two of them stood in dead silence as they each felt, but couldn't see—not with their breasts in the way—as Ruby's arousal made itself apparent. Twelve achingly hard inches of girlcock swelled thicker and thicker as blood pounded into it, her sister's slippery abs ten times too tantalizing to ignore. It crawled higher, up and up, until its entire hot length was pulsing between their stomachs. Cradled in by two girls' slippery, warm skin.

"Uh," Yang said. "Ruby. Is…that you?"

Ruby met wide lilac eyes. She almost died on the spot.

"Sorry," she squeaked. "I just—you were moving, and—"

"Hey. Relax. I'm not mad, I'm just…making sure there's not a tentacle monster in here, or something." She forced out a laugh, but then swallowed. Despite playing it cool, Ruby could see she was flustered. How couldn't she be? Even Yang had limits. Purple eyes flicked down, she couldn't see anything, not with their boobs in the way. "Damn," she said. "That's really all you? Feels…even bigger than it looks."

Ruby had no clue how to reply to that statement.

Yang coughed. "What I'm getting at," she tried again, "Is you definitely won't be leaving any girlfriends unsatisfied." She cracked a grin.

At Ruby's continued red-faced mortification, Yang also blushed.

"Right. Okay. Don't make jokes about the dick," Yang said. "Just ignore it." She seemed to say it more to herself than Ruby.

"Where are we?" Ruby asked, desperately focusing on the practical. Not on the fact her cock was pushing into Yang. "What is this place?"

"A trap? No clue. Traps aren't even supposed to be a thing in Rifts. Much less whatever this is." She started to wiggle again, trying to get her arms up and out, with them trapped at her side.

Which meant her sister's tight, bumpy stomach started massaging Ruby again. Her cock slid against each ab, trapped between two layers of hot and sticky skin. Pleasure arced through her with enough strength to make her hips thrust forward completely without intention. Ruby's cock slid an inch higher up Yang's stomach—and with a lot more pressure. Her toes curled. Ruby's thoughts went white at the sheer ecstasy.

A low, keening moan escaped her lips.

The two of them froze again.

Terror shot through Ruby. She'd just…moaned. Because Yang's stomach had been rubbing against her. Even worse, she'd thrust into Yang. She'd thrust her cock against her sister.

What was wrong with her? Why was Yang's body arousing her? That shouldn't happen. They were family.

"Well," Yang stammered. "Thanks for the vote of confidence. I do have a pretty banging bod. But, um, stay focused, Ruby."

Her attempts to defuse the situation worked only halfway. That Yang was acting unperturbed—even if only semi-successfully—in a situation like this did a lot to help. But far from cured Ruby's embarrassment.

"Y-You're not the one being rubbed into," Ruby struggled to defend herself.

"Dunno about that. Your thighs are doing some work down there, pipsqueak. How about you, uh, stop squirming so much, yeah?"

Ruby hadn't realized she had been. She forced herself to still. Meanwhile, the fact she'd been pleasuring her sister with her thigh sent electric little jolts through her entire body. She became hyper-aware of her body's positioning—especially of where her leg pressed between Yang's legs. Her cock throbbed against Yang's stomach.

"Alright," Yang said. "We really don't have a choice. I'm gonna have to get us unstuck. You can deal with that?"

"Don't have much choice," Ruby mumbled, red-faced, unable to meet her eyes.

"Right. Just, uh, tell me if I need to stop. Wouldn't want any…accidents."

Wouldn't want her little sister cumming all over her, Ruby translated in her head.

She felt suddenly dizzy.

"Here I go," Yang said.

The movement began again.

She was helpless to do anything as her sister worked herself free from the tunnel. Squirming right against her and around her, tits rubbing, abs teasing, pussy rocking back and forth along her thigh. Pleasure grew, edged on by guilt and embarrassment. Hot waves of bliss. Her cock grinded against Yang's stomach, electric sparks flickering up and down her shaft.

By the time Yang wrangled both of her arms up and above her, creating just an inch more space for the two of them, Ruby's cock was threatening to burst, a warm feeling spreading through her stomach, both familiar and not. A new kind of encroaching climax.

"S-Stop," Ruby gasped out.

Yang stilled immediately. Ruby stood there, knees shaking, as her cock pulsed and throbbed and burned with heat. Pleasure ebbed at her vision. Yang said something, but it sounded like static. Ruby panted and gulped, whimpering in pleasure.

They stayed that way, Ruby panting hot air, for a good minute or two. Finally, the stimulation lessened, her cock giving one final angry pulse before calming. Not growing soft, but not threatening to burst either.

She let out a long, slow breath.

"Uh," Yang said. "Better?"

Ruby couldn't look at her. "B-Better."

"You next," Yang said. "Get your arms out. Then we can start to shuffle our way up. It's slippery, but if we work together, we can force ourselves free."

Getting her own arms out was much easier; Yang had broken the seal with her previous efforts. Having something to focus on made the sensations down low easier to ignore too.

Soon enough, they were using the full extents of their aura-enhanced strength to find some tiny bit of friction against the wall. Thankfully, the stone here wasn't as coated in whatever lubricant the slide had been covered with, so it wasn't an impossible endeavor.

Ruby made it up and out first. Silver eyes flicked around the darkness. The funnel-shape of the slide had been shaped in such a way to throw them into this cylindrical cavity, but there was more to it. It continued on. They hadn't yet finished the slide downward.

Ruby helped Yang out, and just when the blonde placed a knee against the slippery surface, their tenuous grip failed them.

All there'd been to do was keep heading down, anyway. Once more, the two sisters tumbled and careened down a long, dark slide.

It spat them out into a proper cavern, this time. They fell from the ceiling about nine feet, but with aura to protect them, the impact wasn't pleasant, but not painful, either.

And maybe because the universe was laughing at them, their landing positions were extremely unfortunate.

Ruby hit back-first, legs spread. Yang fell on top of her, face into Ruby's stomach—which meant breasts straight onto her cock.

Blinking, the blonde looked up at Ruby.

Yang had landed in such a way that Ruby's cock was sticking between her breasts.

That sight…did some things to her. Seeing her older sister laying atop her, tits pressed into her lower stomach, twelve inches of already-aching girlcock piercing two soft pillows. And Yang's lilac eyes flicking between her face, her cock, and further down, where the slim, pale rod sprouted from between a soft embrace.

Yang scrambled up and off her.

"Sheesh," Yang said, face burning red as she waved her hand back and forth, forcing herself to laugh—to break the tension with humor, like she always did. "That's, uh, a coincidence and a half, ain't it? My bad, Rubes."

Coincidence?

No, Ruby doubted that at this point. This Rift was definitely going to kill her. Just not in the usual way.

Ruby didn't scramble to her feet like her sister. The past few minutes had been too much. She'd been fighting too intense of pleasure for too long. She panted as she looked down her body. At her twitching cock. After rubbing all over her sister's abs, and then being inside her tits, Ruby was even closer to exploding than when they'd been stuck in the hole. Waves of pleasure threatened to overwhelm her.

"R-Ruby?"

Ruby lay there, cock twitching violently, a string of precum drooling down her shaft. The knowledge that her sister's eyes were on her cock, watching it threaten to come undone, was its own aphrodisiac. Hot air escaped Ruby's mouth in loud pants, the noise filling the otherwise silent cavern. Yang's joking finally stopped. She stood there and watched with the deepest blush Ruby had ever seen.

Somehow, somehow, Ruby forced herself not to finish. To not squirt her first load all over her own chest and face right in front of her sister, without even stimulation to make it happen. Her shame simply wouldn't allow it. Though that shame had also been working to take her apart in the first place.

Swallowing, Ruby forced herself onto unsteady feet.

"Um," Ruby said, pretending nothing had happened. "S-So. Where are we now?"