"Twilight," Thunderbolt said, "you only need a small sample. I can get that from one shaft."
The implication was clear to Twilight. She took the few steps closer to Thunderbolt and, after a quick look back to make sure the centrifuge was working, she energized her horn and took over stroking one of Thunderbolt's shafts.
"Couldn't resist?" Thunderbolt didn't need his fantasy anymore. Watching Twilight's magic glow wrap around his shaft the moment his talons left it, he was almost overwhelmed by desire as she gripped the whole thing just like her insides had.
Each time she stroked and rippled her magic around Thunderbolt, he made little grunts and growls. At first she was worried she'd hurt him, but the look in his eyes as she rubbed him off sent shivers down her spine. He didn't just look horny, he looked hungry for anything she'd give him.
The hunger in his eyes only grew as she watched him—gazed back at him while she worked. There was a possessiveness in his look that had nothing to do with the games she knew Rainbow played, but was the simple act of a male coveting the female he was with. It was wild and untamed, and it made Twilight feel further aroused.
Holding the cup in his free talons, Thunderbolt could feel his end approaching quickly. Being handled in such a way, by someone he felt a close connection with, did things for him that had his blood boiling. He looked deep into Twilight's eyes as the first hint of pressure attacked him deep inside his groin.
With the heat radiating from Thunderbolt's exposed shafts increasing, Twilight could feel and see muscles tightening and preparing him for the big moment. A perverse desire filled her, and even as he held the little cup up to his free shaft, she pressed her snout forward and made a hole in the end of the magical vagina she was stroking him with.
Thunderbolt's eyes widened as he realized what Twilight was going to do. The sight of her getting ready to drink his essence. The situation was just what he needed to shove him over the edge. Tightening all the muscles in his rump and back legs, Thunderbolt aimed the shaft he was controlling at his belly and the waiting cup.
Feeling the tension in Thunderbolt's belly, Twilight had but a moment to remember how much he'd pumped into her other end before he was unloading. The first two jets of dragon seed had her mouth feeling full, and Twilight rushed to start swallowing it. She barely got the first swallow when another two jets filled her snout to capacity.
Gulping faster, Twilight's eyes widened when she barely got another load down her throat than he filled her mouth full again, and another quick blast had the pressure literally shoving his seed down her throat and leaking out the sides of her mouth.
A traitorous cough was all it took to make Twilight jerk free of his shaft in an effort not to drown in dragon seed. And, of course, that meant she took the last three quick blasts in the face. Screwing her eyes closed, Twilight Sparkle experienced her first facial. She wasn't sure why, but the ridiculousness of it had her laughing.
Surprised at a touch to her face, Twilight let Thunderbolt wipe most of the mess clear of her eyes so she could see again. "That was a much better idea when I didn't think about how much you'd make." She looked up at Thunderbolt and couldn't fault him for productivity—his belly and the talon that'd held the cup were all dripping with his seed.
"Will this do?" A deep, rumbling laughter trembled in Thunderbolt's throat as he held out the little cup—filled to the brim—to Twilight.
Giggling, Twilight used her magic to take the cup from Thunderbolt, accidentally snorted in her enthusiastic laughter, and coughed as the resultant intake of air had more dragon semen in it than was possible for ponies to inhale safely.
From her neck up, Twilight was soaked with Thunderbolt's semen. Caked in it, even. "I need a shower…"
"There's another way to get clean. Hold still." Arching his back and curling his neck, Thunderbolt leaned down and licked around Twilight's nose and snout. Again and again he licked, cleaning up his mess and slowly restoring Twilight's coat to its clean, if damp with dragon spit, self.
Personal and tactile, and more than a little sensual, Twilight found herself leaning into each lick as Thunderbolt worked to clean her off. She turned her head a little so she could see her centrifuge, and floated the cup of semen over and began working on it with her magic.
Purring more and more, Thunderbolt nuzzled and licked at Twilight until she was clean, though her scent was now distinctly draconic. "I can clean up the rest."
"The rest?" Twilight looked up at Thunderbolt, then traced where his eyes were looking to his two jutting shafts and wet belly. "Oh. Uh…" Biting her lip, Twilight was still well aware of how much of him she tasted, and how hot it was to gulp down his seed direct from the source. "I-I think I can help with that."
Leaning forward, Twilight nuzzled at Thunderbolt's clean belly—just beside one of the streams of his seed—then started licking with her much smaller tongue. The taste and smell was more intense now, but it was something she'd acquired a liking for already.
"You don't have to, but that is…" Thunderbolt was disarmed by Twilight's work. He slumped back and his muscles slowly lost all tension as she crawled up onto his chest and kept cleaning him. When she got to his shafts, however, things changed.
Twilight's eyes widened when, on her second lick on one of Thunderbolt's shafts, he licked her aching vulva. She hadn't had any inkling of how horny she'd been, but the moment he'd started lapping at her, she knew her motor had been running already.
Warmed to her task, Twilight ensured every scale and every nodule was bathed only in saliva before moving on. In the back of her throat she started to make hungry little whines thanks to Thunderbolt's ongoing attention.
Twilight had Thunderbolt clean, but he didn't care. The mare spread out atop him continued to make cute sounds, and Thunderbolt like knowing she was enjoying herself. When he heard a door open nearby, he paused in his attention and turned to look.
Marble stared at the two on the floor in front of her. She knew Thunderbolt at least a little, and knew Twilight a bunch more, but she didn't know they had something going on. "W-W—" Words failed.
Spinning her head around to look at Marble, Twilight felt her cheeks grow hot and quickly tucked her tail down to hide herself. "Marble! I—uh—we were just doing a test to find out if Thunderbolt is fertile with humans—err, ponies, I guess."
Just staring, Marble wasn't stupid enough as to be unable to join the dots. "You think you might be p-pregnant?"
Twilight carefully stood up and climbed off Thunderbolt, then turned sideways so Marble could see her belly. "Dragons do this thing where they seal their, uh, semen inside with a plug-thing. It made me worry just a bit."
"Oh! Several species do that. Pigs for one." Marble walked into the room and approached Twilight, her trepidation lost in a sea of scientific curiosity. She reached for Twilight to feel her belly, then paused. "It's okay if I… touch you?"
Thunderbolt, realizing that the funtime was over, rolled to his belly and watched the two females. Each was smart and sexy in their own way—he found himself quite liking smart and sexy.
When Twilight nodded, Marble reached carefully to her friend's—and sometime lover—belly and felt the obvious swell there. "I'd need to take more measurements when you aren't—full, but I can definitely feel bloating. How long ago did you—?"
"Less than an hour. Probably about half. Uh, how long was it meant to take?" Twilight looked at Thunderbolt.
Purring softly, Thunderbolt flicking his tail once, then twice. "Two hours at least. The others—"
"Others?!" Marble froze as she realized she'd cut in on him. "S-Sorry."
"It's okay. Others, plural, have had it last at least two hours since I became fully me."
"I was going to do an antibody test first of all. See if my T cells react to his sperm and try to annihilate it." Walking over to the centrifuge, Twilight used her magic to levitate a pipette and take a sample of her split blood's clear fluid. "His blood was the fascinating thing. I'm not completely sure, but given its green color, I'd say his body uses copper to transport oxygen."
"Like ocean invertebrates? That's fascinating! So you're saying the parasite doesn't depend on the type of oxygen-carrying cell at all?" Marble reached for her own pipette and began preparing a sample of the green blood cells in the centrifuge.
Thunderbolt contented himself with watching the two women work, at least until his curiosity got the better of him. "So you have things in your blood that kill sperm?"
"Well, technically they kill anything that they think shouldn't be there. We're testing to see if they consider your sperm to be… something that shouldn't be there. If that happens, there will be no chance of conception because not only will my immune system kill your sperm, but even if I manage to conceive, it will kill the embryo too." Twilight used her magic to adjust the microscope.
"I'm testing human blood too. Can't be too careful, and it might be different to pony blood," Marble said.
Moving slowly so as not to startle the women working, Thunderbolt walked carefully across the floor of the musk-scented basement so his head was beside Twilight's. "Can I see?"
A further blush hit Twilight's cheek and she moved aside to let Thunderbolt in. "What you're looking for is a clustering around those large, worm-like cells."
Marble stopped her own examination of dragon blood to watch the source of said blood. He was huge, and the smell coming from him was distinctly male, something she was always unsure of in the past, while it smelled musky, she also wasn't adverse to it.
"There's a lot of them," Thunderbolt said with a purr in his throat. "There's also a lot of that clustering."
Twilight wasn't exactly trying to shove Thunderbolt out of the way, but when she moved closer to the microscope he shifted to give her ground. Looking through the eyepiece, Twilight could see activity that indicated that the T cells were reacting to the spermatozoa. "This is great news!"
His head grabbed in Twilight's Magic, Thunderbolt didn't struggle as she brought his face down to her level and kissed him. Thunderbolt smiled and pressed his tongue forward just a little—just the tip—and tasted his essence in Twilight's mouth. The kiss was much more fulfilling for that little fact.
Breaking the kiss, Twilight stared at Thunderbolt with a relieved and slightly blushing expression. "So we're safe."
"You're safe," Thunderbolt said. "And, yes, we're safe. I still need to be careful if I find another dragon."
"It looks like humans are safe too, however much human I still have in me." Marble lifted her face away from the second microscope and reached a hand up to brush one of her ears.