Sweetie was there for her younger self the moment she first stepped into Lucid's Dream. She kept the filly model, along with her old mane style. When you were a copy, you needed everything you could get to differentiate yourself.
At first she spent only a few minutes awake at a time, with Sweetie following a few steps behind her and monitoring everything she did. That saved her more than once, since Sweetie could step in and use a few commands to stop her mind from spiraling out of control.
Nopony in the real world could possibly react in time, or understand what they were seeing. But Sweetie lived here too—she knew the simulated mind as even Lucid Storm couldn't. She knew this mind in particular, since those were some of her strongest memories. Waking up after her death, confused and mechanical—she remembered what that was like.
In time, her younger self no longer needed constant monitoring. She could run somewhere in the real world, using an old brain connected to a maintenance terminal. That limited her abilities—that computer could not frameshift to experience more time when there were more resources, though it could slow to match the pace of time in Lucid's Dream.
Mostly that meant Sweetie needed to write some special code for her, manifested as a magical necklace, which would slow to match the instance, or eject her if her hardware couldn't keep up.
It would be easier if they could just upload her with everypony else—but she didn't want to tell Lucid about her new sister. What oblique conversations they had on the subject confirmed what she already feared—that the bat wanted nothing to do with the idea of copying minds.
"Ponies need their illusions, Sweetie. We don't really understand how consciousness works—we assume there's something ineffable about it, something that would be lost if we modified it. Nopony wants to think they're just a pattern playing over again. But if we start forking minds in there—even if we had the resources—that illusion starts to break down.
"We're already facing pressure to stop from Luddites across Equestria. They want to shut the Dream down, think no one is really alive. That I'm exploiting the hopes of desperate ponies for wealth and fame... or worse, trying to get them to kill themselves. That's the real reason I limit contact between Equestria and the simulation."
So she kept her head down, relying on Capacitor to mask her input and output traffic. After all, she was using official hardware. No reason to kick her out of the system.
Scootaloo indulged the whole thing with few objections, though showed clear discomfort whenever the copy spent too much time with her. So maybe Lucid was right about that part of pony psychology—few wanted such direct evidence of just how ordinary they were.
That wasn't the only painful separation she faced. Sweetie couldn't let Rarity find out about her, for the same reason that she had to hide her from Lucid. If her sister learned about a copy, there was no telling what she might do. So she kept her younger self from living too long in the Dream. A day or two here and there, without ever knowing that time moved differently for her.
A sensible decision—Sweetie hoped—but also a heartbreaking one for her younger self. It meant she lost every connection with her life before, except for an older version of her friend who was uncomfortable to be around her, and also dating her older self.
But she was a tough filly. Sweetie had endured a crippling disease, braved a new technology to escape it, and more. She could survive a little hardship, for the eventual promise that ponies would understand.
After a few subjective years, her younger self hadn't grown any older—but she had made some new friendships with other fillies and colts, all victims of accident or disease just like Sweetie herself. Thanks to them, she didn't even have to share Sweetie's home with her anymore, so long as she came by for regular checkups every few days.
The Dream itself changed right along with them, growing larger as new ponies arrived, and the resources available to them increased. Eventually, the whole town got together for the first event of its kind: a pony leaving.
But it wasn't Sweetie. She rejected that path to stay with Scootaloo, who might not have a body for some time. She could live in the Dream for a while longer, even if it meant the world passing them by outside.
She missed disasters in Equestria—missed her sister moving out of Ponyville on her ambitious plan to expand her clothing line to a national brand. She missed the retirement of Equestria's Diarchs, stepping down from their roles to allow Twilight and Cadance to rule as the nation's newer princesses.
They didn't miss Apple Bloom’s wedding to a pony she'd met during a dance class, though they could only watch through a camera, and didn't get to taste any of the wedding treats.
The Dream expanded too. They didn't have a princess, but as computers got better, the world itself could get more detailed. Identical streets and an out-of-focus town turned into a city of vibrant lights and color, split into districts that recreated various parts of Equestria, and times. Those elderly ponies inside recreated the simpler times they'd been born into.
Meanwhile younger ponies blurred the boundaries of tribe and magic into impossible creations that could never exist in the world outside—sky cities where every pony had wings, spectacular castles and recreations of books and movies.
Naturally Scootaloo wanted to live in one of those, and Sweetie came along. With new colors and wings along with her horn. In a simulated world, no pony could be bound by inconvenient things like tribe.
Ponies came and ponies left. At first the arrivals were a steady stream, then a flood. Eventually, departures went from a city-wide celebration to a dedicated platform in the city train station, where friends would share a few treats together before a pony got their new body.
Sweetie herself found a place—not in the wild, experimental world of art and creation that Scootaloo fell into, but as a more practical part of her new world. Plenty of digital minds needed doctors. Some had arrived incomplete, or fractured as time went on and the reality of their digital existence set in. At first that work was clandestine—but soon she earned recognition for her notes on the subject, and later formal publication. Within the year, she had a full-time position in the role, with a practice of mental medicine connected to every version of Lucid's Dream.
It earned her significant income in the real world, where bits and scarcity still mattered. More importantly, it earned her recognition and satisfaction in her digital life, every time she saw a pony she had helped continuing to live, instead of dissolving into fragments and vanishing from the city.
Eventually, bodies were so easy to manufacture that more ponies began to leave than those who arrived. The same technology that made them could also be used to keep living ponies still alive, after all. Eventually, she ran out of excuses.
"You deserve to be here," Lucid said, over a virtual conference call. "Everypony asks about you. All these synthetic ponies, and the first one is nowhere to be seen. I've had bodies for you and your partner for six months now—what are you waiting for?"
What was she waiting for? Sweetie had no answer for him right away. She made some excuse about a patient and slipped away, soaring on pegasus wings to her marefriend's room high in the clouds. These sorts of spatial incongruities were just another part of her world, after all.
Scootaloo might not be there right away—but thanks to the strange properties of time in the Dream, Sweetie wasn't waiting for long. Seconds almost, and the mare touched down in the clouds. She settled her wings closed, brushing up against Sweetie. "What's wrong? You look upset."
"Upset..." she repeated, circling over the clouds. Even years of living here couldn't quite make cloud walking and flight feel normal. She would appreciate them far more for going most of her life without.
"Not exactly. Just... Lucid talked to me again today. About leaving. I'm expected up there. We are." That last part was a lie, and they both knew it. Scootaloo's aunts stayed in touch with her, but her parents rarely had. She had few connections left in the world above, and fewer still that would be expecting her.
Scootaloo nuzzled her neck, as tender as the mare ever had. "You don't want to go. It's okay to say it."
Sweetie Belle didn't say it, but she did nod, avoiding her marefriend's eyes. "I wish I could visit instead of living up there."
"You can," Scootaloo said. "Lots of ponies visit after leaving. They just can't frameshift anymore."
Without that ability, a pony could only move at the speed of time on the outside. Weeks could never pass in days, only the other way around. "If I go up there, will you come with me?"
She didn't want to ask, because part of her already knew the answer.
"My life is here. I don't want to go up there—get a job, work for bits to afford some tiny little apartment. Or worse, dragging you down with me." She opened both wings, lifting into a hover. Scootaloo flew like a skilled pegasus—probably better than any real one. Physics would get out of your way in Lucid's Dream, if you asked politely enough. "I'm happier here. I think you are too."
She had no answer to that. Her work wouldn't be possible without abilities an external existence couldn't afford her. Only by bending time could she preserve many of the worst cases that arrived at her clinic. How would she live with herself when that transition cost somepony's life?
"Lots of ponies want me back there," she whispered. "My sister wants to see me again, probably lots of ponies do."
"I didn't ask what they wanted," Scootaloo said. "Can you look me in the eye and tell me you want to go back?"
She tried—and she failed. Lucid's Dream was an Equestria unto itself. Many old friends were outside—but she'd lived far longer inside now.
"They want me back..." she began. "They worked so hard to save me when I got sick. That's kinda how this whole place got here." Then she froze, staring down over the balcony at her castle far below. Sweetie Belle—the original, without wings—was just walking in, humming a lonely tune to herself as she went.
"Maybe there's another way."
It wasn't as simple as flipping a switch, of course. She had to talk to Capacitor, now a senior technical director at the company, and persuade him to help with the transfer. A few ponies, like Lucid, would have to know. Maybe they would let the older Sweetie talk to her family on the outside again—maybe she would have to pretend to be somepony else until they arrived in the Dream.
Either way, it felt only fair. She'd barely even suggested the idea to young Sweetie Belle before the little filly lit up, bouncing eagerly up and down with delirious energy.
"I don't have to pretend?" she asked, after explaining everything to her. "No dressing up or anything. No telling ponies that I'm a big scientist."
"Nope," Sweetie promised. "Official story is, you gave those memories to some pony in here to keep doing your work. You have to be digital to do it anyway, so... it won't seem strange."
The little pony embraced her, hugging Sweetie tight on the station platform. "What do I tell them about you? Who helped me?"
Sweetie Belle shrugged. "Whatever you want to tell them. I think I'll go by Harmonic for a little while. Just tell them I'm a friend. Mom and Dad are older now, and Rarity too... but they still love you. They never did well with me being digital anyway. They want to be out in the real world—so go out there, be real. Be Sweetie Belle again."
"I will!" she promised, hugging Harmonic again. "I'll message you every day, and tell you how it's going! Maybe one day I'll get a marefriend too! Then you can come to our wedding like you went to Apple Bloom's."
"Maybe." She let go, urging her onto the platform. "I'd like that."
She watched her step onto the train, and the automatic doors closed behind her. Soon she was gone, off to a world Harmonic had left behind a long time ago.
They would both find their happiness. Equestria was a different place—there was plenty to go around.
The End