Author's Notes:

This chapter is almost entirely sex. Thank you to everyone who helped turn this fic into something resembling readable and the entire staff of the Clocktower Society! Have fun!

The Terra Nova Research Labs were finally clean, stocked to accommodate every conceivable need (and a few more besides), and completely empty - save for two people idly debating in the middle of it.

Sunset gave Twilight a sly look. “You want a hypothesis? If I put my mouth on your clit and suck, then you will come so hard you see stars, because I like to think I know what I’m doing.”

Twilight swallowed. “Oh.”

Sunset smirked at her lazily, then blinked. “Actually, that’s not a bad idea.”

“Um-”

“You have your necklace on, right?”

“Yes?” It hung just below Twilight’s white-and-gold collar, the pendant resting lightly at the top of her sternum.

Sunset hopped off the table. “We should make sure it’s safe to wear during an orgasm.”

Twilight winced. “...Instead of making everything in the room float. Yeah. But wait, aren’t the, um.” She blushed. “Aren’t the others pretty good indicators of that?”

Sunset counted off on her fingers. “Rainbow doesn’t wear hers much because she can’t get a good workout with it on, I don’t wear mine because it’s creepy, Applejack does lose control when she comes but it’s hard to separate that from a normal physiological reaction, I don’t know what’s up with Rarity so we don’t have that data point, Fluttershy’s power doesn’t really have an ‘out-of-control’ setting, and Pinkie....” She trailed off.

“Pinkie kind of defies science,” Twilight agreed. “But what would we do with the information once we had it? We’re the only people it would possibly affect.”

Sunset gave Twilight the blandest look she could possibly muster. “I’m trying to come up with a cute excuse to have sex, I don’t think we have to adhere to scientific rigor so much.”

“But scientific rigor is hot,” Twilight mumbled.

Sunset paused. Her smirk came back. “Well, in that case.” She snagged one of the lab coats off the hook on the wall and shrugged it on. “Who says you have to know what I’m testing?”

When she looked back at Twilight, her sub’s eyes were wide and her mouth slightly parted. Sunset took it as a good sign. “When I get back, you should be undressed and ready for me. We’ll need--” And she rattled off several implements, enjoying Twilight’s mounting confusion as the list went from “spreader bar” to “digital thermometer.” “Three of each, if you can find all of it in here. If not, don’t worry. Once you’re done, sit on that table with your hands behind your back.” She paused just long enough to see Twilight starting to obey, then swept out of the lab down to the main room.

She took a moment, once she was out of sight, to firm up the vague idea she’d been working with into an actual plan. She’d left the room mostly to give Twilight time to go around in circles wondering what was going to happen, but since she’d told her to get extras of everything, they did have the space for a control. Hmm.

Rainbow, when Sunset found her, was doing wind sprints across the short end of the main cavern while Fluttershy sat at the other end with a book. Sunset eyed both of them, then got out of Rainbow’s way and just went to talk to Fluttershy first; she had a feeling that would be faster for everyone involved.

“Hello, Sunset.” Fluttershy had her mask on, a delicate black butterfly shape that stood in stark contrast to the rest of her pastel wardrobe. It matched Rainbow’s black collar in color and decoration.

“Hey, ‘Shy,” Sunset said, and paused as Rainbow reached them and turned to walk back across the room. “I was wondering if you and Rainbow wanted to help with an experiment Twilight and I are conducting.”

“Oh, that sounds like fun,” Fluttershy said, and set her book to the side. “What do you need us to do?”

Sunset explained the short version of her idea, elaborating when Fluttershy asked various questions. Eventually the paler girl nodded and raised her hand, beckoning Rainbow to come back. Rainbow, who was already sprinting, put on an extra burst of speed and skidded to a stop in front of both Doms. “‘Sup?”

Sunset repeated the basic run-down.

“You know my snatch works, right?” said Rainbow, unimpressed. “Like, I totally could fuck people, I just don’t want to.”

“The whole point is not to come,” Sunset pointed out.

Rainbow’s expression cleared. “Well let’s go then!”

Sunset laughed and began to walk towards the Fire of Devotion, now blazing brightly enough to light the entire cavern easily, and then some. “That’s a surprising amount of enthusiasm for someone who just got told she won’t get any orgasms.”

Dash snorted. “Are you kidding me? This sounds like a contest, and if there’s one thing I like, it’s winning. This is gonna be a breeze.”

Fluttershy hid her giggle behind her hand.

Once they reached the Fire, Fluttershy gestured and Rainbow sprang upwards, sprouting wings at the peak of her jump. Sunset was impressed in spite of herself; for someone who had only spent the last year or so intermittently having wings, Dash’s transition from jumping to flying was amazingly smooth.

“How many of these do we need?” Rainbow hollered down.

Fluttershy looked at Sunset.

“Ten?” Sunset guessed loudly. It was probably a vast overestimation, but better to have too many than too few.

Rainbow held her sweatshirt out with one hand like she was collecting flowers in an apron, and poked at the bottom of the Fire. Several tiny embers broke off, and she caught them neatly in her makeshift pouch before returning to the ground, a blissful expression on her face.

“Waaaaaaarm,” Rainbow purred, to Fluttershy’s amusement.

“Do you want to carry them there?”

“Yeaaaaaaah.”

Sunset smothered her own laughter as Rainbow moved the embers to her front pocket for ease of travel. “Well, your sweatshirt’s not on fire, so there’s that question answered. Let’s see how worked up Twilight’s gotten herself.”

Twilight had, in fact, not had time to get herself worked up, and the first view the trio got of her was of her standing on a chair to reach a box sitting above one of the cabinets.

“Twilight,” Sunset said.

“Aah!” said Twilight, and dropped the box. Rainbow zoomed to her side and caught it. “Oh. Sorry. Thanks.”

“You didn’t follow my instructions,” Sunset said mildly.

Twilight fidgeted. “I - I was trying, but I couldn’t find the-”

Sunset cut her off. “I told you to be sitting on that table naked with your hands behind you. Is that what I’m seeing?”

Twilight realized she was still standing on the chair and climbed down. “No, but-”

“Twilight. I’m disappointed.”

“I didn’t have time!” Twilight protested automatically.

Sunset crossed the room in four quick strides, palmed a carabiner off the table, and spun Twilight around and locked her wrist cuffs together behind her before the other girl realized what was happening. A mean little part of her wanted to kick the back of Twilight’s knees to force her to kneel, but the floor was hard stone and too rough to indulge that impulse safely.

Instead, she stepped back and folded her arms. “What did I tell you to do?”

Twilight glanced back at her, confused. “Get the stuff out, get undressed and sit on the table?”

Sunset sighed, maybe overdoing it a little. “You’re incredibly smart, Twilight. I told you to find the items we needed, but not to worry if you couldn’t.”

Twilight blinked once before understanding lit up her face. “Oh! The important part was the sitting on the table, not the getting stuff!” She visibly replayed that sentence in her head and her expression wilted. “Oh.”

“Oh.” Sunset arched an eyebrow. Damn, but Twilight was cute when she learned something new.

“I, um-” Twilight looked around at herself, and then the floor, and then Sunset. She almost had her intentions stamped on her forehead, so clearly did she broadcast “I would do that now but I am tied up but this is my own fault, oh no what do I do.” “...Sorry,” she tried.

Sunset relented. “You’ll do better next time, won’t you?” Twilight nodded vigorously. “That’s good, because I had a surprise for you, but now you’re going to have to wait to find out what it is.” She considered. “Try and get your clothes off like that. You can lean on things if you need to. If you can’t do it without uncuffing your hands or getting help, you don’t get to come today.”

Twilight gave her a wide-eyed look and started squirming around.

Sunset wanted to watch, but since this had gone from nonsense banter to actual science, she had to help set up the rest of the equipment. “Could I get you guys to help me with this part?” she asked Fluttershy, who nodded. “Okay, so which way is closer to the... okay. Here, can you-?”

When all was said and done, six small stations dotted the room, each with variations on the theme of “an ember of Devotion with a thermometer and an infrared camera pointed at it.” The remaining four embers sat in a glass bowl, while Rainbow sat on the table next to them, looking anticipatory and shucking her clothes off.

Sunset checked on Twilight. She’d made a formidable amount of progress for someone with her hands cuffed together; her skirt, shoes, leggings, and underwear were in a pile on the floor, and she was currently frowning at her button-down shirt.

“It could have been worse,” Sunset pointed out, when Twilight noticed her watching. “You could have worn that sweater-vest thing.” She leaned one hip against the side of the table, grinning shamelessly. Honestly, she wasn’t sure what she would do in Twilight’s place, and was curious to see what Twilight could come up with.

What Twilight came up with was a pencil, which she held between her teeth. She sat against the edge of the table and her eyes unfocused - it took Sunset a moment to realize she was concentrating on undoing the buttons at the ends of her sleeves, to give herself more room to move.

Once she had that, she tugged on each sleeve with the opposite hand, so that the front of her shirt rucked upwards and she could reach the top button with the tip of the pencil. Unfortunately, all she managed to do was draw some squiggles around and on the button. She didn’t have enough dexterity to slide the button back through its hole while keeping the fabric taut.

Drool started to slide down the pencil, and Twilight finally abandoned it with a frustrated noise. Sunset started forward to help her, but stopped short at Twilight’s, “I can get it!”

“Okay,” she said, amused and somewhat skeptical.

Twilight craned her neck forward, but she wasn’t flexible enough to grab the buttons directly with her mouth, and her collar stopped her from touching her chin to her chest. She gave up on that and shrugged the shirt back to where it was supposed to sit. “I like this shirt,” she muttered.

“Hey, Twi,” Dash said.

“Wh - eep!”

Rainbow cracked up, and would have fallen off the table were it not for Fluttershy. Twilight, who had been focused on her clothes and mostly facing the other way, had failed to notice Fluttershy cuffing Rainbow’s hands above her head and attaching a spreader bar to her ankle cuffs. Rainbow fell on her back on the table, still giggling. Fluttershy, who was smiling too, gently covered Rainbow’s mouth with one hand, and held it there firmly until Rainbow subsided, the muscles of her back and neck relaxing. She blinked slowly at Fluttershy.

Twilight hadn’t been able to look away for long, and Sunset was unrepentantly staring at all three of the other people in the room. Twilight’s mouth was open slightly, her eyes wide and drinking in every detail.

Fluttershy took her hand off Rainbow’s mouth. Rainbow licked her lips and rolled her head to look at Twilight. “See if you can step out of it.”

Twilight gave her an utterly confused look, and then it clicked. She bent backwards, then forwards, trying to find a good angle, then eventually crouched. For all that she lacked much muscle definition, Twilight had long arms and narrow hips, and those facts combined with a lot of determined wriggling resulted in Twilight’s still-cuffed hands behind her knees instead of behind her back.

“I’m legitimately impressed,” Sunset put in.

Twilight pulled one leg and then the other through the hoop her arms created, took a moment to roll out her shoulders, and smugly undid the buttons of her shirt. Her bra was the sort that clasped in the front, and she looked very pleased with herself for it. She smiled at Sunset, though she couldn’t stop the edges of it from turning into a smirk.

“Good girl,” Sunset said, and stepped forward to unclip Twilight’s cuffs. “No, no, this doesn’t count,” she added to forestall that balk she could see coming. “I don’t want to mess around with your shirt. Stretch your arms out a little.” She gathered up the various articles of clothing on the floor and stashed them on the counter at the front of the room, then returned to Twilight. “Arms up.”

Twilight glanced at Rainbow, who was chilling in a slightly more elaborate set-up than Twilight had last seen: a rope stretched her arms above her head and anchored them to the table, while a second rope anchored the spreader bar to the floor, so that Dash was more or less pinned on her back with her belly exposed. Twilight studied her for a second, then laid back in approximately the same pose.

“Clever girl,” Sunset praised her, before remembering that most people thought of that as a line from a movie. Oh well. It made trussing Twilight up easier, after which she ducked under the table to grab the handful of leather and metal she’d hidden there earlier. When she straightened, Twilight lifted her head the few inches she could to try and see what was going on.

Sunset put her hands behind her back. “How much of a surprise do you want this to be?”

Twilight stared at her, then at her midsection, as though if she tried hard enough she would be able to see through Sunset. “I want to know!”

Sunset laughed. “Yeah, okay, I should’ve guessed that one.” She brought her hands out, revealing the strappy bridle she’d had made for Twilight. It was spare, with a minimalistic approach to its cheek and brow pieces. The straps were thin and a plain brown, though on a whim Sunset had gotten the metal bit tinted lavender.

Twilight gasped.

“You want it on you?”

“Yes.”

Sunset pulled Twilight’s ponytail out of the way and slid the bit between her teeth. Twilight, a little overeager, grabbed onto it, then held her head up to let Sunset buckle each pair of straps snugly.

“Is that comfortable? What’s your safe signal?”

Twilight rapped her knuckles against the table three times in a row.

Sunset smiled, then on impulse kissed Twilight. With the bit in the way, she mostly tasted steel and salt.

“Can we get going yet, or what?” Rainbow complained.

Fluttershy put a hand on Rainbow’s shoulder. She didn’t use any force, or say anything aloud, but it still prompted a, “Sorry,” from Dash.

Sunset grabbed an ember out of the bowl. “So the whole point of this is pretty much to see what... well, what happens when we do different things.” She grimaced a little. “As much as I’d like to have a more detailed hypothesis than that, we really don’t have any idea how this thing works. Every five minutes, Fluttershy and I will take notes on each ember, including the ones on you and Twilight here. Rainbow is acting as the control, and won’t come if she can help it. Twilight, you can come as much as you want, but that doesn’t mean I’ll stop.”

So saying, she followed suit (heh) in taking her clothes off, leaving them with Twilight’s, and double-checking the equipment was working while she was at it. Then came the fun part.

She started slowly, mindful of Twilight’s inexperience and well aware of the effect of prolonging foreplay. She ran her hands over Twilight’s body, following everywhere she touched with the ember, and for a moment wishing intently that she still had a unicorn’s built-in levitation magic. Twilight made quite a number of wonderful noises, but seemed mostly confused.

That is, until Sunset dipped the ember lower, skating across Twilight’s groin before immediately moving away and going back to circling. Twilight groaned, realizing where this was going, and mock-glared at Sunset, who responded with the most innocent smile she could manage with a straight face.

This was going to be fun.

Much to her dismay, she did eventually have to leave off torturing Twilight to take notes on the other embers. She moved the one she was holding away from Twilight’s vulva and let it rest just below her sternum. Twilight whined.

“Oh, c’mon,” Rainbow said. “It’s not that bad.”

Everyone in the room gave her the same unimpressed look.

Fluttershy and Sunset switched places, making a circuit around the room as they did so. The readings on the other embers had mostly not varied, save for a slight increase in temperature on the ones closest to the side of the room facing the main cavern, but Sunset was itching to get her hands on that video data.

That, however, would have to wait. “So I take it you’re doing fine,” Sunset guessed dryly.

Rainbow blew out a long gusty sigh. “Uh, yeah. This one time I rigged up a vibe so it would stay put and then waited to see if it would do anything? This is like that but warm instead of... buzzy.”

“Huh,” said Sunset, writing most of this down. "Fluttershy's not really doing much with you, though, is she?"

"No. It'd be weird." At Sunset's arched eyebrow, Rainbow continued, "I don't really... like coming? Honestly it kinda hurts. I rub one out once in a while but it wouldn't really be fair to make Flutters guess which five minutes in the next two months I'm gonna be horny enough to get off. So it's just a soft limit for us. Anyway, the point is we'd both feel creeped out if she was actually trying."

“So you wouldn’t say it’s having any effect?”

Rainbow shrugged, which was kind of interesting to watch, given her position. “Not physically, but, like. I feel super subby and all I’ve done is lie here. Usually it takes an hour’s workout to get me like this.”

“Well, it is the Fire of Devotion, not the Fire of Orgasms,” Sunset said absently. Half her attention was on the paper in front of her; the other half was focused on Fluttershy talking quietly to Twilight.

“Oh, I know, and you’re doing so well, but you’re not mine, and it wouldn’t be very nice of me to touch someone else’s things, would it?”

Rainbow gave Sunset a wry look. “This is gonna be a short experiment, isn’t it?”

Sunset tapped her lightly with the eraser end of the pencil. “You shut up.”

Fluttershy appeared next to Sunset just in time for Rainbow to start melodramatically whining about “she hit me!”

“No, she didn’t,” Fluttershy said serenely. “Unless you want me to consider that my new definition of the word ‘hit’?”

Sunset made her way back to Twilight, tuning out Dash’s frantic backpedalling. “You doing okay?”

Twilight looked up at her with a gaze like honey and nodded.

“Good.” Sunset climbed on the table and swung one leg over Twilight’s torso. “‘Cause now it’s my turn.”

“Mm!” said Twilight, and picked her head up as far as she could, straining forward.

Sunset laughed. “Stars, you’re cute. C’mere.”

It took some maneuvering, but Sunset got herself scooted up so her knees were on either side of Twilight’s head and her weight was mostly braced on her hands. Twilight got impatient and licked the inside of Sunset’s thigh, which was all she could reach.

Sunset giggled and gently eased herself down. She didn’t want to overwhelm Twilight.

Oh, fuck, fuck, somehow she’d forgotten the bit in Twilight’s mouth, fucking Tartarus that was fantastic. She rolled her hips without meaning to, then did it again on purpose when Twilight gave her an enthusiastic noise. “You can’t have done this before,” she gasped. “How are you this good at it.”

Snickering came from her right. Sunset flipped the bird in vaguely the correct direction, which just made Rainbow giggle harder and Fluttershy join in.

“Fuck it, whatever.” Sunset arched her back and reveled in Twilight’s eager exploration, jolting when her tongue knocked the metal against Sunset’s clit. Twilight noticed, and messed with the bridle so she could do it again, and then in sequence.

“Have I mentioned how much I love it when you learn things,” Sunset growled. “Yeah, yeah, ffffffuck, I’m almost - ah!”

Her orgasm was the quick bright thing it had always been, and she moved as soon as she could to give Twilight room to inhale, catching her own breath at the same time. She felt herself drip on the table and couldn’t muster up the energy to care.

She kissed Twilight slowly, as thanks, tasting her own musk and come against the clinical steel.

“That was fantastic,” she whispered. Twilight hummed. “I think you deserve a reward for that.”

She hopped off the table, grimaced, then fished out a clean washcloth from one of the cabinets. That would keep the mess between her legs from smearing and drying on her skin, at least. She tossed it onto one of the empty tables before turning her attention back to Twilight.

First things first: she retrieved the ember from Twilight’s belly, prompting a protest that got summarily ignored. Hmm, what was the best way to...? Gingerly, she touched the ember to the fold of flesh above Twilight’s clitoris, only to draw it back, startled, when Twilight yelped and jerked.

“Uh, are you okay?”

Twilight smiled sheepishly around the bit and nodded. “Suhsi’ive.”

Sunset switched tactics, and slid the ember between Twilight’s labia, holding it nestled against the entrance to her vagina. She brought her free hand up to play with the swollen, slick pink above that, trying to not-quite-touch Twilight’s clit - at least, until Twilight whimpered and squirmed, and there went that plan.

Sunset swiped her fingers across Twilight's cunt, deliberately without precision. She tapped and tugged gently, making a note of which movements made Twilight buck and moan involuntarily. Twilight, shuddering, arched like a drawn bow when she came, and at that, Sunset backed off, satisfied.

For a moment, the only sound was Twilight’s panting. Sunset leaned heavily on the table, setting the ember to the side, and rested one hand on Twilight’s hip to ground them both. After a moment, she stood back up. “I’m gonna untie you now, okay?”

Twilight made an incomprehensible noise, and when Sunset looked at her, she shook her head, not quite lucidly.

Sunset pet her belly softly, shifting so she was sitting next to Twilight on the table. “Shh, it’s okay, I’ll be right here, I just want to let your shoulders relax. That all right?”

This time, Twilight nodded, if reluctantly, and Sunset reached up to undo the clip holding Twilight’s arms above her head. Knowing the muscle would be sore, she took Twilight’s arms by the joints, one at a time, and brought them slowly back down to a normal position. When she was done, Twilight sighed and leaned her head against Sunset’s thigh.

Sunset glanced at Rainbow and Fluttershy, whom she’d pretty much forgotten about. Rainbow was watching with detached interest, smiling to herself; Fluttershy had both hands over her mouth to suppress any noises she might make but was clearly also grinning irrepressibly underneath them. When she saw Sunset looking, Fluttershy took her hands away to mouth so cute while gesturing at Twilight.

I know, Sunset mouthed back, then turned back to the object of her affection. “Wow, that’s a fast trip to subspace for you, huh?” she murmured. She was pretty sure Twilight was only vaguely aware of what she was saying, but talking gave her something to latch onto while Sunset undid the bridle and other restraints. “Don’t think I’m not gonna remember that, Sparkle.”

“Hmmmmmmkay.”

“Come on. Future You will be happier if you clean up now. I’ll help.”

“So I take it the experiment’s done,” Rainbow guessed dryly.

Sunset snorted with laughter despite herself. “Uh, yeah. I’ll get Little Miss Loopy’s account out of her later. Thanks for hanging around and helping.”

“No problem,” Fluttershy and Dash said in unison.

“Mmmm-not... loops,” Twilight said.

“Sure,” Sunset agreed.

“Cold.”

“Yeah, okay, here, up, lean on me, there we go.” There were aftercare rooms along the hallway towards the main chamber, and most of them had showers. Magic: best source of immediate hot running water ever.

“I can bring your clothes over if you’d like,” Fluttershy offered. Sunset shot her a grateful look.

“That would be amazing, thank you. Are you two okay here?”

Fluttershy glanced back at Rainbow, who was fiddling with her cuffs, tongue sticking out the side of her mouth in concentration. “Yeah. Thanks for inviting us. I’ll come by once Dashie gives up.”

“Hey,” Rainbow protested, albeit distractedly.

Sunset shared an amused look with Fluttershy, then stumbled out of the room, supporting Twilight heavily as she walked them both in the direction of a hot bath.

“Mm, Sunset,” Twilight said vaguely.

“Yeah?” said Sunset, but didn’t stop walking, since if she did she was probably going to sit down in the middle of the hall and not get up again.

Twilight turned her face into Sunset’s neck. “Love you,” she mumbled.

“I love you, too.” Pause. “...Twilight? You don’t have to say yes, but I’d really like to change your collar to black. Would that be, um, do you think you would like that?”

“That would be really nice. Yeah. Yeah.”

Neither of them could have stopped the smiles that spread across their faces if they’d tried.