I'm going to continue this as a series of small stories. This one is less explicit, and focuses more on in universe justification for what will follow. I hope you enjoy it!

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It was not unusual for Twilight’s library to be lit well into the night. The brilliant unicorn was frequently burning the midnight oil, researching whatever currently had caught her interest. Tonight, however, she was not alone in her candlelit study. She sighed, and looked up across her oaken desk at her longtime friend. Rarity sat across from her, a blush on her cheeks as she fidgeted. Twilight’s stare softened, and a sigh escaped her lips.
“So, Rarity, tell me again why you thought this was okay.”
The ivory unicorn looked into her friends violet eyes, and took a deep breath.
“Well, when I found the spell, I thought it would be useful for me to improve my small scale embroidery. It was purely for the boutique, you see. But then Spike offered to help me, you see…”
“Yes, you used the spell on Spike. When I finally got him to tell me, he refused to go into detail. Do you want to explain what happened?” She asked, her tone getting a little sharper.
“Oh, no nonono, darling. It wasn’t anything like what you’re thinking. He just looked so cute, you see, and I was just overcome with this… desire. I just wanted to….to….” she trailed off, her cheeks blushing furiously as she searched for the right word.
“You wanted to what? You didn’t do anything… like that, with him, so what did you do?” Twilight responded, her curiosity coming back to the forefront.
“I just wanted to… play with him. To have him serve me, totally and completely... I’m sorry, this is terribly awkward to try to explain…” She fidgeted some more. “You see, it’s just...seeing him so small, and the way he looked up at me like I was some sort of.... Goddess…” She breathed, her heartbeat quickening even at the memory.
Twilight looked down at her desk, her hands coming up to rub at her temples.
“Okay, I guess I can kind of understand that. What… what did you do with him?” She asked, a hint of worry seeping back into her voice.
“Well, I had him in my hand, you see, and he was rubbing my palm with his tiny claws. It felt so very nice, so I asked him if he would be willing to give me a teensy little footrub.” She looked down at her lap and bit her lip. “Honestly, that’s all it was. I just set him down at my feet and he climbed up and started rubbing. It felt so wonderful, better than anything they can do at the spa.”
Twilight let out a sigh of relief. “Okay. I believe you. So after your fun with Spike, you wanted to do it again?” Rarity nodded, her blush deepening even further. “So you got several stallions to agree to you using the spell on them, and you asked them permission first, or else the spell wouldn’t work…” Twilight slapped her hand down on her desk, her mind made up.
“Okay, I know what we need to do. If these… stallions… are still willing to stay with you, then there’s no problem here. There’s no law against grown ponies doing what they want to together as long as it’s consensual.” Twilight stated, standing up and walking around to Rarity’s side. Rarity looked up at her friend’s face and gave her a small smile. “So, just take me to where you have them and we can have this solved in a heartbeat!”

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As the two mares walked in through the front door of the Boutique, something that had been bugging Twilight became too much for her to keep bottled up.
“So, Rarity, I was wondering… Why didn’t you tell me this before? Why did I have to find this out from your sister?” Her voice dropped from a low volume to a barely audible whisper as she tried to keep the pain out of her voice. Rarity snaked her arm around her fellow unicorn, pulling her in close to her side.
“Oh, Twilight, I’m sorry I didn’t come to you sooner. I was just worried that with what happened with Spike, you might not be very pleased with my… current obsession, as it were. And I really didn’t want to lose my little pets…” Twilight gently reached up and pulled Rarity’s well manicured hand off of her shoulder.
“Let’s not get too far ahead of ourselves just yet, Rarity. I’m here to make sure that they’re willing to stay here. I’m not upset with you about what you did with Spike, but the stallions,” She said with extra emphasis, “are a separate issue.”
“Oh, I know that, darling.” Rarity laughed quietly, trying to show confidence she didn’t completely feel. “I just know that they aren’t going to have an issue with staying.” Her grin started to fade as they reached the door to her bedroom. She took a deep breath, and pushed the door open.
The unicorns stepped into the room and turned on the light, revealing the decorated box-turned-house that kept her new cohabitants safe. She clicked her tongue lightly, and the tiny stallions started to file out of the carefully carved doors. Twilight let out a gasp and fell to her hands and knees, carefully crawling towards the miniaturized ponies. Rarity stayed back, making her way over to her luxurious bed and sitting on the corner.
Twilight noticed immediately that the stallions were amazingly at ease with her crawling towards them, in fact more than one of them was staring openly at her now exposed cleavage. Where she would normally be mortified at the slip up, she noticed that there was distinctly something… different about the gaze of a stallion at 2 inches tall versus one that stood taller than her. Her heartbeat quickened slightly as she crouched down about a foot away from the gathered “pets”. They gazed up at her expectantly, no fear or hatred evident on any of their faces. She cleared her throat and made sure her knees were squeezed tightly together to prevent a straight line up her skirt for the crowd.
“So, my name is Twilight Sparkle, you may know me from around Ponyville. I’m here to ask you a couple questions, so if you could please be honest with me we can get started.” The little ones nodded up at her, and a couple of them sat down and started to get comfortable.
“Okay, so first things first. How many of you are still wanting to stay here? Just raise your hand if you do. You can be honest, I’ll make sure you get home if you don’t want to be here anymore.” She gazed expectantly at the little ones before her as they started to raise their hands one by one. Shockingly, not a single one didn’t have a hand raised. Even more, they didn’t look at all like they weren’t being sincere.
Twilight blinked a couple times, before giving her head a little shake. “Well, Rarity, looks like they don’t want to leave. You must be quite the host.” Rarity laughed nervously and scooted a little closer across the mattress. Twilight turned her attention back to the stallions as one of them stepped up to her knee. She couldn’t help being overcome with wonder at how small he was as he reached up and tapped on her kneecap. She looked back to Rarity for direction, confusion evident on her face.
Rarity giggled and waved her friend on. “Go on, darling, just pick him up. He obviously wants to talk to you.” Twilight looked back down and placed her hand down next to him. He climbed up on her palm, his bare feet tickling her soft skin. Her heartbeat sped up again at the novel experience, and she took a sharp breath. She gently closed her fingers around him and lifted him up to her face. Her eyes focused on the stallion’s face, which she couldn’t help but notice was smaller than any of her fingernails. He was vaguely familiar, she recognised him as one of the new arrivals from out of town. He smiled and wiggled until his arms were free, so he could cup his hands around his mouth.
“Miss Twilight, I didn’t have anywhere to stay before Rarity offered to help me. I don’t have any complaints about how she’s treated me, only…” He trailed off, causing Rarity and Twilight both to lean in.
“Yes?” They both asked in unison.
“... It would be nice if we could get some variety in our days. Nothing against Rarity’s bedroom, but most of us have been here for more than a month, and it would be nice to see some...other ponies…” He started to blush furiously and look away from Twilight.
Rarity couldn’t stop herself anymore and slid down off of the bed, scooting over to Twilight’s side.
“I have been a little selfish in locking you up here with me. I was afraid of getting anypony else involved, but I didn’t even stop to think about what you might want.” She reached out with a finger and gently rubbed the top of his head, causing a dopey smile to cross his face. Twilight couldn’t help but giggle at that. There was something just so… adorable about the way they hung on the every action of the giant mares.
A thought crossed the bookish unicorn’s mind, one that she normally would immediately try to bury. Something about the stallion, though, made her decision a little different than it would have been if he were still at his natural size.
“I have an idea.” She declared, drawing the attention of all of the stallions as well as Rarity. “ We have established that you are here of your own volition, and that some of you may be wanting a little more variety in your daily activities.” A chorus of tiny nods confirmed her statement. “So if that’s the case, then I think there’s only one way to go about this.” She looked over at Rarity, who had picked up one of the little guys and was petting him nervously.
“I think it’s time for you to share with your friends.” She grinned, and Rarity smiled in relief. “Now who wants to come back to the library with me?”

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