When Twilight made it all the way back down the stairs, she wasn’t terribly surprised to see that Fluttershy had yet to set hoof in the syrupy mess all over the library interior. Luna was remaining outside with her, having a pleasant conversation with the nervous pegasus. And much closer to hoof, Celestia was lazily hovering through the air of the library, looking over Twilight’s defensive systems. Every ward and trigger had been laid bare by gentle yet powerful magic, allowing the alicorn full access to everything inside.

“Very precise work here, my student... I think I have a sufficient view of the situation that we can clean up without damaging your system.”

“I... Really, Princess? Normally, I just clean it all manually, or make whoever set it off do it as punishment.”

A brief hum of thought from her mentor.
“Yes, I believe so. Come, let us discuss the idea before we set it in motion- Better overprepared than under, in this sort of situation.”

The next few minutes passed in a nigh-incomprehensible (to outsiders) blur of discussions on magical theory and application, at which point they nodded to one another.
“Well, now that we have the theory hammered out, let's get to work! How about you create the framework, and then I'll power it?”

“Sounds good, Pri-... Celestia.”

A moment of concentration, power lighting from one point to the next. With the gentlest touch, she probed out to make sure their work would not interfere with the delicate intricacy of her warding system. Its safety assured, Twilight began to pour out energy, layering fierce calculations atop rapid guesswork and her almost intimate knowledge of her home, quickly wrapping every inch of the room in a tight lattice of radiant purple light. Slowly, the bulk of the magic faded out of the entire network until all that was left was a massive web of filaments, conduits waiting for power.

And power they received, poured out from one of the most potent vessels in Equestria. Celestia concentrated alongside her, taking her spell and putting it to use-- The sun’s very heat licked out from the minuscule wires, causing the sap across every surface to dry, crack, and then break into powder as the process continued. By the time they were finished all that was left was a miniature desert made of powdered resin, which was quickly whisked up, gathered, and sealed into a small jar (no sense in wasting resin without reason). The steam withdrawn from it all was ushered out the windows, and finally the protective sheets over the bookshelves could be removed.

“Thank you! That would normally have taken hours to get rid of.”

Celestia smiled as she gestured to her sister, bringing the other ponies inside.
“Yes, well, we barely have hours before the announcement this evening... And I do believe you are missing a rather crucial element, are you not Luna?”

The Lunar diarch stopped, looking between Fluttershy, Twilight, and her fellow ruler.
“I... I do not think so? We have quite clearly made all arrangements without fail, gathering to our side many important ponies, all required permits, and the decorations as well as a feast... Not one thing has been forgotten!”

“Ah, yes, and you had your assistant to remind you of all these things, did you not?”

“Of course not sister! My dear assistant is... still in... Canter... oh. Well, blast.”

--------

It was extremely unnerving, for Fluttershy at least, to see Luna so flustered. Celestia was just grinning as her sister ran around frantically, and Twilight seemed a bit confused. Fluttershy on the other hand... She didn’t like seeing such a strong and confident pony acting as worried as a... Well, as worried as a Fluttershy. The only time it was normal for her to see that kind of nervous half-sad half-angry expression was when she was looking in a mirror. Seeing it on Luna’s face hurt a bit. She wanted to be helpful, but what could she really do? This assistant, whoever they were, was all the way in Canterlot. Hopefully, they could just do without...

“Well then, I will be off! My return shall be swift, so do not fret over my absence.”

Fluttershy frowned. Yes, well, it was totally to be expected that...
“Wait, what?”

Luna looked at her with a smile, her nervous expression from before gone as if it had never been.
“Yes, we’ll be back... Before the tenth hour, I believe. Plenty of time!”

“...Um, Luna, you’re talking about going to Canterlot. And back. In three hours?”

Her lover was looking somewhat incredulous now.
“Yes. Why?”

Before she could question the sanity of the situation, Twilight jumped in to do it for her.
“No offense Princess, but that’s ridiculous! Taking a train from here to Canterlot would practically be an overnight trip! And flying... Well, I don’t doubt that you are extremely fast, but if you have to arrive, get this ‘assistant’, and come back with them in tow, I just don’t see how it could be possible! You’d have to be travelling through something other than normal space... Wait. Waaait.”

Celestia finally let loose laughing as Luna chuckled, both of them turning to head out the door.
“Well, my faithful student, you got it right on the nose. We try not to let it be too well-known to the public, but the two of us have... Other avenues of travel at our disposal. Would you care to watch?”

Fluttershy was only half-listening to the conversation, thinking about what Luna could possibly be doing. If she wasn’t flying through “normal space”, like Twilight said, she would be... What? Was it dangerous? Was it scary? She had no idea where the pony she loved was about to go, or how, and it seemed ridiculous to just let her go like that, sitting here like an easily-frightened lump on a log. So she put a hoof out to stop the Lunar Princess, looking at her with an obvious question in her eyes.
“L-Luna, can I... go with you?”

“Dear Fluttershy, why would thou wish to do that?”

She scuffed a hoof across the threshold of the door, trying to make eye contact but failing.
“Well... It sounds lonely. Travelling in some special way only you know how, there’s probably not much company, right? So I could go with you, if that’s alright. With you.”

“Certainly! I had not considered it before, but I would treasure thy company as I travel.”

Her confidence about being helpful during the trip slowly waned as Luna looked up to the sky, seemingly staring straight at the sun. There was silence for a moment or two, and at the same time Celestia was leading Twilight back into the library.

When Luna spoke again, it was soft, reserved. It reminded her of the night she saw Luna’s moonrise first-hoof.
“The stars are... always there. Everypony is blinded to their presence in the day, for they are far outshone by the sun. But when one has the knowledge, it is simple enough to look past the sun, to see them glittering in the grandest distance. And with their grace, we will fly. Are you ready, my dear?”

“Y-yes.”

“Then take my hoof.”

Tentatively, carefully, holding her breath, she reached out and placed her hoof on Luna’s. There was a moment of disorientation, and then it felt like the ground, the air, like everything was melting away from them. Moments later, Luna took off, and she followed out of instinct. There was a blur, a faint hum on the edge of hearing... And then they were gone.

--------

Her sister’s departure was no surprise to her- After all, Celestia had seen her do it thousands of times, had been there the day she finally developed the technique. Her own method was similar enough that they had travelled together from time to time. Even then, they were always separated by...

“Princess? Can I...”

“Twilight. Please.”

Her loving student looked confused for a moment, and then blushed as the issue hit her.
“...Celestia. Can I ask what exactly that was? I’ve never seen magic quite like it before!”

“That was because it was not magic at all, Twilight. It was something... more primal, I suppose one could say. More innate. It only makes sense, now that I think of it, that I show you how it was done.”

Every exhaustive minute of planning for this day was swept into irrelevancy when she saw that spark in Twilight’s eye. There was nothing more pleasing to see than the mare’s love for learning, her lust for knowledge, her insatiable... curiosity.

“R-really? Yes! I mean, yes, please, do!”

With a harsh -snap- she spread her right wing to its full length, and looked into the sky. It was easy to fall back into the old forms, to let her concentration drift as she recited the theory. In her heart, it was still that first day, millenia ago, when she codified the idea and made her first jaunt across the space only she could touch.

“The sun shines down on me. It shines down on all things, at all times. The moon, after all, merely reflects the light of the sun- Although that does not make it a lesser thing, for that reflected light must guard the night alone. But either way, the sun shines down... And I look up. I see the sun, I know the sun, I feel its light and warmth. Moreso than any other pony, I am close to it... And if I need to be, I can get closer.”

Celestia paused to let Twilight soak it all in, and then bent her wing back towards the mare.
“Twilight, hold on tightly.”

She felt the hoof, tentative on her feathers, and then another. Twilight wrapped her forelegs completely around Celestia’s wing, and from there climbed up to her back. She sat down, muzzle near her mane, the closeness making them both shiver. A quick check to make sure that Twilight was properly positioned, and then Celestia was ready. Following suit with her sister, she tensed, focused, and leapt.

--------

In something that felt paradoxical, it was just like she had never left... Even the very first time. Strange how one could feel that way about a place they had never been to in the first place, but it was true. ...As true as anything could be, in this world between worlds. The golden light shone not from the sky, but from every direction at once instead of ‘just’ from her Sun. Her hooves skimmed the edges of tall wild grass, always just far enough away that she could never manage to identify them. The environment, all hills and valleys, stretched on forever, sky full of brightness and a wind that was hot without being stifling. Everything had a bright scent she had (eventually) learned that other ponies associated with her mane. Distinct, like spring and summer condensed and focused, but never strong enough to distract from the task at hand.

She could see a good landing spot on the horizon, even though they had only taken off a few seconds ago. After all, a few seconds didn’t mean the same thing here. Travelling much longer would be... problematic. She squinted down the path, a clear-cut line amongst the otherwise lush fields. The sun was setting- Perpetually, that is. Celestia could hear a breath of (she assumed) stunned awe behind her, and she smiled.

“Perhaps we will come back again some time. But for now... These, Twilight, are the solar plains.”

Focusing her will once more, Celestia attempted to dive downwards, touching down in the infinitely-tall and yet infinitely-short grasses. Even though her hooves never went any deeper than the tips of the stalks, a moment later, the light faded and she found firm land beneath her. Ten seconds of flight meant they were roughly... Mmmh, a mile outside of Ponyville, give or take. Nothing too taxing to fly back manually.

“So, what did you think Twilight?”

No response, although she noticed that the unicorn was rocking against her back. Was she nervous, frightened? This might have been a mistake...

Celestia turned her head to face her lover.
“Twili-”

Her question was cut off as her student bore down on her, a sudden burst of motion catching her completely off-guard as Twilight lunged. They hit the ground a second later, Twilight’s kiss hot with fury and an insatiable fervor.

--------

They were back in normal space and time and air and light but she didn’t care she couldn’t care, because Celestia was right there and wasn’t being tended to at every moment and that just wouldn’t do. She leapt, pressed forward, pressed herself on and around the mare she loved, adored, followed... The heat and the smell and the light were still all around her, it was as if she hadn’t left at all, that same rough buzzing through her mind and the taut nervous energy in her muscles. She kissed with every ounce of effort she had, could feel her magic crackling and snapping off of her horn with every furious lick and each loving thrust of her hips. There was something slight on the edge of her perception, maybe somepony saying something, but that wasn’t important. Twilight kept lunging and loving and living, everything so vibrant and sharp and wet and-

“TWILIGHT SPARKLE!”

A sudden cold snap fell over her, everything growing terribly still for a moment. The golden haze in her head receded, and Celestia was looking at her. She looked frazzled, and if she had a hair out of place, Twilight could only imagine how she herself looked. Her teacher / lover wasn’t angry or sad, which, considering everything she had just done, was impressive. Instead, she looked at her with a faint smile, the kind you put on when you aren’t sure how badly you just bucked up.

“Twilight... I apologize. Are you alright?”

Words were trying to leave her mouth, but she was finding it a little difficult to speak. In the back of her mind, she realized she had split one corner of her lip with how vigorously she had kissed the Princess.
“Y-yeah. I think so. I just... Wow. Wow. Did you...”

“No! I mean, no. No, that was just... I will explain later, when we have time and access to some good books. Suffice to say, there can be some unexpected side-effects of travelling on those plains.”

Her full attention was, as always, on what Celestia was saying. But also as always, a piece of her brain was running calculations and adding up details in the background, her personal ‘backburner’ for the exclusive cooking of ideas.
“Over them.”

“I’m sorry?”

Twilight snapped back to the conversation with a jolt.
“What? Oh! Hahaha, sorry about that. I just got a little sidetracked. I’m so sorry if I acted... badly. A second ago.”

Celestia was looking at her with a dour little grin, and walked closer.
“Twilight, love?”

“Yeah?”

The kiss was sudden and unexpected, and managed to carry a portion of that earlier insane mindless passion that had been rolling through her just a minute ago.
“Never apologize for that.”

She smiled at her teacher, nodded, and the two of them began the walk back to Ponyville. It probably wouldn’t take too much convincing to get Celestia to take her back through the plains on the way back, maybe land directly in the bedroom... No, save it. There is such a thing as over-indulgence. Plus, Spike and the Crusaders are probably still in the house! Hopefully not still in the bath- After that, I certainly need to use it.

Her sudden apple-red blush went unnoticed, or at least not commented on, as they trotted back.

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Authorial Note: Credit for the picture used in this chapter belongs to John Avon, and reproduction rights for said picture belong to Wizards of the Coast.