Rather than lamenting about the rather unfortunate results of her experiment, Twilight saw this as an opportunity, now she had all the time in the world to collect, collate and categorize everything about the human body from psychology, physiology, digestive system, reproductive system, everything she could ever hope to know about humans. Then when she had finalized all of her findings she could fix the mirror and become a pony again, simple!
She decided to start with the basics, outward appearance.
Bipedal
Teeth suggest omnivorous diet
Hair present on head and genitalia
Breasts present on the chest
No tail
Things called "hands" on the end of each arm, similar dexterity to dragon claws
No hooves
Small plates known as "nails" on the end of each "finger" and toe
Short muzzle
Ears that have various shapes of indeterminate purpose
Lack of fur
Lack of horns or wings
Much larger than ponies, similar stature to teenage dragons
Well, that just about covered all the main things Twilight knew simply by looking in a regular mirror, so she thought about what the next logical step would be. That's when it hit her, she had seen all the physical differences with clothes on, but there may have been other differences she hadn't noticed because they were hidden under them, she had to look at her human body naked. Rather casually, Twilight began to remove her clothes until she was completely nude and looking in the mirror, after examining her body she noted down that humans seemed to lack a cutie mark that indicated their talents. It was as Twilight was observing herself that Spike had decided to walk in, carrying a tray that had some cookies and a glass of milk on it, he put the tray down before actually realizing that Twilight was seemingly checking herself out in the mirror.
Spike just stared, he had seen Twilight as a human before and he was fully aware of the experiment she was conducting, but he hadn't exactly expected to see her naked. He didn't know why, but there was something different about being naked as a human than when she was a pony, but he couldn't quite place it... then he realized it, she looked like a dragon. Well, obviously not exactly like a dragon, there were no scales, tails, wings, horns or claws, but other than that she looked fairly similar to a quite gorgeous dragon girl. The idea of Twilight being an attractive dragon girl stirred something inside him, something he was unfortunately unable to stop or even necessarily hide as his two reptilian dicks quickly began to harden in preparation to breed.
Spike began to panic, he couldn't allow Twilight to see him becoming erect simply because he thought she looked slightly similar to a dragon, he managed to silently sneak out of the room and close the door then sighed in relief as he went to find somewhere private so he could calm himself down. What Spike was rather unaware of was that Twilight had already seen him anyway, she was looking in a mirror so of course she was going to see his reflection, she wasn't stupid. Though she was surprised for two reasons, one being why Spike had found her body so alluring and two being, why in the wide wide world of Equestria were his penises so unusually huge?! That gave Twilight pause... were they unusually huge? The reproductive system of dragons hadn't been documented since... well, ever. She knew that dragons had two penises, she had raised Spike after all and physically speaking he didn't appear to be any different to any other dragon, though being that they were so massive even when not fully erect made her question the facts somewhat. She made a note to herself to see if she could study dragon reproduction at a later date as she continued to study her own body.
Once Twilight was sure she had had learned everything she could about her human appearance, she figured that she deserved a rest, this project had taken months of precise calculations to make sure she could actually even conduct the experiment in the first place and since she wasn't going to be a pony again anytime soon on account of the broken mirror, she saw no reason why she couldn't take it slow and pace herself, it would also be beneficial study-wise, she didn't want to miss anything that might be important. Thinking about dragon reproduction actually gave her an idea as to what phase she should move onto next in her foray into understanding human beings, human reproduction. This did mean she would have to somewhat explore herself more intimately to see how the particular sexual organs worked and how similar or different they were to that of a pony, but nothing was too embarrassing in the quest for knowledge!
After having the cookies and milk that Spike had brought her, she made her way to her bedroom, still completely naked. She figured her bedroom was as good a place as any to start getting a little more physical with her human body, especially considering the particular part of the body she was going to be looking at. The first thing she did was take a close look at it, physically it was smaller, the vulva was less pronounced and the clitoris appeared to be something that was ever present, which to Twilight suggested that winking was not a function in the human vagina. Then she brought her hand to it, sensitive, very sensitive and her body reacted somewhat immediately as Twilight felt her human pussy becoming increasingly wet and lubricated which made her quite... distracted. It didn't take her long to forget about her project, she said she needed to relax, plus masturbating might give her more of an insight on human sexual stimulation and orgasm, that was the excuse she gave herself for rubbing her pussy anyway.
Twilight let out soft moans as she sped up her hand movements, panting and sweating as she masturbated as fast as she could, all pretense of discovering new information thrown completely out of the window. A couple of minutes later Twilight bit her lip to stifle a loud moan as she experienced her first orgasm as a human being, she couldn't tell if her orgasm was particularly intense because she was human or because of some other reason, but at that moment she didn't really care, she was too busy experiencing the pleasure coursing through every cell of her body. She let out a deep breath and allowed herself to fully relax on her bed, basking in the afterglow of a very long overdue orgasm, being so focused on this project had left here rare opportunity to find a secluded place to pleasure herself. Once she was fully recharged she sat up only to meet eyes with none other than Spike, who had just walked in upon her reaching orgasm and had been frozen in place ever since with two very large, very hard and very desperate, throbbing, veiny and unmistakably erect cocks.
Twilight tried to act casual about it and said "Hello Spike! How are you feeling?" The obvious answer to that would have been "horny", though that didn't seem like the best answer to give.
Spike was beyond embarrassed and just went "Um... I think that... maybe I should just go and-"
Spike was interrupted when Twilight, a bit louder than she meant to, just went "NO!" Spike stopped dead in his tracks and gave Twilight a quizzical and slightly confused look. Twilight cleared her throat awkwardly and said "I mean, no, no need to leave Spike. In fact you've actually arrived at the perfect time".
Spike was perplexed "I have?"
Twilight confirmed "You have. You see, being in this human body, I've decided that one facet of the species I need to study is the reproduction system and ever since seeing your... *ahem* ... equipment earlier, I've also seen fit to study the reproduction system of dragons at some point, but seeing as I'm here perfectly... available... and you're there perfectly... ready... I suppose you could say that this would be the best opportunity to kill two birds with one stone, so to speak".
Spike didn't want to get his hopes up, but he was pretty sure Twilight was actually asking him to have sex with her, he looked her in the eyes and said "So... just to be sure..."
Twilight already knew what he was about to ask and said "Yes Spike, I'm asking you to have sex with me, don't you want to have sex with me?"
Spike panicked "No no no! I do! I do! I just wasn't expecting it".
Twilight giggled "Excitable one huh? Come on Spike, get in the bed with me and we'll just... feel our way through it I suppose". Spike did as she asked and, still with two fully hardened cocks ready to be serviced, climbed into bed with Twilight. Twilight, still trying to make out this was for the sake of scientific discovery instead of the simple fact that she just felt like boning Spike, went "OK... I think it might be appropriate at first to um... lubricate you for ease of access to my... well, y'know the place where these things go...". Twilight may have been horny, but she was still a nerd. She took hold of one of Spike's penises and stroked it up and down, admiring its shape, he had a fairly sizable girth, not to mention a good amount of length, Twilight was almost nervous about the impending sex.
As she stroked one penis she took the other into her mouth and moved her head up and down as she gently sucked it, Spike simply groaned as his heart started thumping in his chest, feelings of deep-rooted lust and instinct coming to the forefront of his brain. Spike reached a claw forward and placed it on Twilight's head before applying some pressure and manually directing the speed and depth of her blow job, Twilight simply let out a small moan and allowed Spike to push her head up and down, obediently keeping up her affectionate sucking. After a minute or so she let Spike's cock out of her mouth with a *pop* and stopped stroking the other one, Spike wasn't too happy about this and actually snarled aggressively. Twilight rolled her eyes and said "Relax big boy, lay back so I can ride you", clearly not fully understanding that depriving a horny and hormonal dragon during the height of the breeding season was probably a bad idea, not to mention dangerous if things got out of hand.
Spike did as he was told as Twilight got on top of him in reverse cowgirl position, before she got started she looked back and said "For you to... well... let's say "finish", do I only need to stimulate one of your penises or-"
Spike interrupted her and in a deep gruff voice pretty much commanded "Both".
Twilight said "OK... let's give this a try", she gripped one of Spike's cock as slipped it into her pussy with relative ease, it was his second one where the problems started. Due to the size difference, getting one cock into Twilight's love tunnel was easy, but squeezing in a second one would be the difficult part. Nevertheless, Twilight wasn't put off and attempted to get him in, with no success whatsoever. Try as she might, Spike's other cock just couldn't fit in next to its twin, constantly sliding away from Twilight's hole. Twilight sighed and said "Sorry Spike, but it looks like- Ah!"
Twilight got the surprise of her life when Spike finally stopped being patient and rammed his second cock up her ass, gripped onto her hips and started pushing her up and down on his cocks. Twilight groaned, not quite sure if she was in pain or not, she was uncomfortable at best. "Spike... slow down..." she said, but her plea fell on deaf ears.
Suddenly Spike sat up and put her into a full nelson, shoving both of his dicks to the hilt in her pussy and ass and silently whispered "GET FUCKED". Which is exactly what she did as Spike abused her body like she was nothing but a rag doll, fire and smoke billowing from his mouth and nostrils. Countless hours and mind-shattering orgasms later, Twilight finally got relief as Spike blasted scalding hot cum into both her holes and practically threw her to the floor like a used tissue, both of them instantly falling to sleep.
Spike woke up with a yawn, it was early morning, the sun was up and Twilight was under the covers completely naked and somehow managing to fit both of his cocks in her mouth as she blew him. As he looked down with a grin she took his cocks out of her mouth and said "Good morning master... how shall I drain your nuts today?"
Spike loved that the rough fucking he had given had somewhat broken her mind, it made it easier to mold her into the perfect sex slave, she hadn't even bothered to fix the magic mirror.
The End
Author's Note
Thank you osmar lael for this story idea! I hope you enjoyed it :)
Twilight scribbled away in her notebook, it had been a long process but the math checked out, it was scientifically sound and she was fairly certain all of the kinks in her previous magic spells had been worked out and that it had been streamlined and refined to a point where the margin of error was so small that the likelihood of something going wrong was a minuscule 0.147296358%. If her hypothesis was correct, the magic of the mirror portal could be temporarily reversed by using a spell that she had specifically crafted so that when it was cast it would reflect back and the hope would be that she would, for a limited time, become a human. Twilight had decided to pursue this for a number of reasons, increasing her magical prowess, understanding of the mirror's magical capabilities, but the biggest reason was perhaps her quest for knowledge, specifically human knowledge.
Twilight used to always visit the human world when there was some sort of catastrophe she could help prevent, but ever since her human counterpart became part of the group in the human world she was quite suddenly not needed. On one hand she felt a little hurt that the human versions of her friends had simply forgotten about her, especially Sunset Shimmer, however it did provide her with an opportunity to study humanity. When in the human world, there wasn't really an effective way to study the human body and translate the data effectively to the pony world, so making herself human whilst still in Equestria became her new project and it was at last in its final stages. All variables had been accounted for, she'd checked and re-checked everything more times than she could count, she was ready.
Twilight put her notebook down and prepared her spell, she had to direct a lot of magical energy into her horn, but if it worked then the short bout of exhaustion afterwards would be worth it, the odds were in her favor. When all of the combined magical elements were present for her spell to achieve its goal she blasted her spell at the mirror, seconds later she felt her body shifting and twisting, thankfully in a rather painless way and after about 30 seconds she was her human self, clothes included. She was about celebrate when she looked in horror as she saw that the mirror had actually broken during the process, that was a problem, it seemed that lady luck had seen fit to create the circumstance that would only happen 0.147296358% of the time. The main problem was that Twilight wouldn't be able to return to her pony form unless the mirror was fixed, which sounded easy in theory but was much harder in practice.
Twilight sighed and said "Well...... fuck."
