A Short Eternal Night In A Library
Author's Note
I used to see myself as having certain mastery over words; sometimes, probably, overestimated, but still here I am. Hence, I may come with eccentric lingual conceptions, like "red" as past forms of the verb "read", or "unicorna" for a female unicorn; also I had to use "alicorna" to stay consistent. Bear with it. 
"Jezve" ("cezve"), in contrast, is not my invention; it's Turkish* 
Of course, if you have some technical comments on the text, feel free to PM me those
So! The welcome party is over, everypony moves to the town hall, scene… But in an unexpected place an unexpected pony appears!
v1.0.3
A Short Eternal Night In A Library
"What did you do with our princess?!"
"Why, am I not regal enough for you? Don't you know who I am? Or is a thousand years that much? Did you not recall the legend? Did you not see the signs?"
"I did, and I know who you are. You're the Mare in the Moon. Nightmare Moon!"
"Well, well, well. Somepony who remembers me! Then you also know why I'm here."
"You're here to…" Celestia, is it really that banal? "To…"
"Remember this day, little ponies, for it was your last. From this moment forth, the night will last forever!"
Shouts of panic were drowned out by triumphant laughter, the howling of the risen wind, and the crackle of lightning. The thunderstruck and blinded ponies didn't notice that Nightmare Moon morphed into smoke and slipped out through a window.
Also, none of them noticed that the guest from Canterlot had left the town-hall—which couldn't be said about the newly-crowned ruler: the only pony who knew something about her deserved special attention.
"Twilight, how can you be so calm?! That was Nightmare Moon there! She's promised eternal night! We must do something!"
"Oh pulease, Spike! I could bet all the books in the library that dawn would come before we'd run out of candles.
"Um, but you don't own the library."
"I know."
"And there is a year's supply of candles in the basement."
"Knowing that."
"And…"
"I know, Spike! Excuse my non-participation in the total hysteria, but I've had a nervous night, and the not-very-well-timed event by Miss Pie, fancy that, hasn't filled me with energy. So I'm not doing anything until I get enough sleep. That is, not sooner than midday."
"Uh, you mean midnight?"
"Whatever. And I recommend you to get a sleep too. Sunrise—new eyes."
"Hm, this reminds me a legend of trolls…"
"Trolls do not exist, Spike. It's just a legend."
"But the Mare in the Moon was just a legend too!"
"The Mare in the Moon has been an established fact in historical science for the whole thousand years! In academic circles."
"She has? I thought academic circles were just a legend."
"Spike, don't remind me the legend of trolls, please," Twilight looked at her companion with a motivating smile.
And yes, meanwhile, they had gotten to the library.
"I have a date with my bed, Spike. What are your plans?"
"Uh, right now I can't sleep."
"Munch a gemstone or two. I'm sure you will feel better."
"Fine, I'll be in the kitchen for a while. Don't turn out the lights please."
"Okay, those upstairs only."
"Okay. Good night, Twilight."
"Good night, Spike."
The exhausted unicorna dragged her body into the bedroom and with delight threw herself onto the bed. She lay there for a while, determining a source of discomfort. It was blowing. She slammed the window shut and rolled over in the bed, drawing the cover, when her eyes met something new in a dark corner.
No. No, no, no!
"Nightmare Moon."
The black mare gleefully opened her mouth, just to shut it in a second, frowning.
Well, at least she hasn't touched my things.
"Twilight Sparkle."
"For the only pony who knows something about me, you are surprisingly unworried... Twilight Sparkle."
"Should I worry?"
"Come on! The eternal night, the returned Mare-from-the-Moon in your bedroom?
"It's not in your interests to harm me. It's not in your interests to harm anypony, even if your desire for revenge is explainable. You cannot lose the only pony who knows about you anything more than the average over Equestria," and with those words Twilight rolled over, facing away.
"Don't you dare ignore me!!!"
"Don't you dare yell in the library!!!" The unicorna leapt upon hooves right in the bed, and both scowled, their eyes on the same level and locked with each other's. Knocking came from below.
"Excuse me, Your Highness," Twilight said between her teeth and went downstairs, considering an appropriate expression on her muzzle before opening the door.
Five familiar pairs of eyes were looking at her.
"Twilight, what's goin' on? You know what to do, don't you?"
"Well, an ancient co-ruler of Equestria has returned from her millennial banishment to the moon after her attempt to stage a coup, caused by lack of attention. At the present time she's spurred on the desire to revenge and prove her significance."
"But how are we gonna beat her and get back Princess Celestia?" That was Rainbow Dash, of course.
Somepony snorted indignantly behind Twilight's back, and she threw a blind pillow (one left there since the party) in that direction.
"Girls, the situation is not critical at the moment. That was just a show of power, we're not going to be faced with tangible consequences. But, to prevent the night from becoming permanent, I need to get a good sleep before working out a plan. So please go home for now and don't surrender to panic."
The four ponies, exclusive of Pinkie Pie who was bouncing away by then, exchanged looks.
"A sole ask… Rarity, can I send Spike to you temporarily? He's being so nervous that he'll devour all the gemstones here otherwise, but your presence has a favorable effect on him. You two could have a chat about Canterlot as well."
"Oh, with great pleasure, darling! A friendly conversation may distract me from the whole disaster."
"And I think Rainbow should see Applejack home, then Fluttershy, and stay at hers overnight."
"But, what about Pinkie?"
"You know her longer than I; can anything really threaten her?
The ponies looked at one another again.
"Great. I'll gather you when the plan is ready. Until then we are not in danger."
"Okay. Tell us when it's time to get done with it."
Twilight mentally patted herself on the back for completing an organizational task. Closing the door, she found her unasked guest glowering out the window.
"How dare they, to challenge the one who can sweep them away like dust…"
The hostess shook her head helplessly.
"Nightmare, it's a wrong policy."
Need to occupy her mouth with something.
"Want some coffee?"
Twilight passed into the kitchen, imagining that it was some kind of a hospitality test; her training partner took place at the table, apparently having found a liveable conception for herself as well.
Out of cabinets came cups, a jezve, and a sack of beans. The hostess was in no mood for bothering with the stove, so the vessel ended up in the middle of a magical whirl.
"Establishing authority by means of terror, you risk becoming a victim of violence from your 'subjects'. And since absolute immortality has yet to be invented, it is a real danger to your life. Although, I have to admit, not many ponies will guess to look for you in a library," she added sarcastically, a grudge in her voice. Nightmare felt a kindred soul in her.
Eyebrow raised, she was watching the magic flame quickly altering temperature and pressure inside the jezve according to some unfathomable plan. In a while, blackened water rose and fell like during usual brewing, gave up its steam, and took a few drops from slender bottles.
The beverage was portioned and served. The guest stared at her cup that was decorated with a precise replica of the night sky; purple steam was spiraling from the coffee surface.
"Refreshes and relaxes. Ideal before bed."
Nightmare took a sip—and narrowed her eyes with pleasure. Twilight by contrast, not being burdened with memories, was drinking undistractedly, from a cup of the same color as her fur, bearing her cutie mark on its side.
It also would be a good thing to discuss downsides of a strong-hoof approach with the risen demon—but not then that the opportunity to postpone everything till things go better turned up.
The last sip uncovered a portrait of Princess Celestia on the cup's bottom, and Twilight smiled tiredly. Analysis and control will overcome this problem.
"Excellently brewed," the alicorna carefully placed her cup down.
"Thank you. I'd gladly discuss more global questions, but for goodness' sake—not today."
After washing the vessels and putting them away, Twilight silently took a course for the bedroom. Nightmare reasonably concluded that they wanted to get rid of her company; basically, she hadn't had plans to stay there for that long, but the drink really turned out calming and relaxing. She followed the hostess, and found her already lying in her bed.
"Oh, I've told you…"
"You want to settle your guest for the night on a sofa?"
"Oh please, I haven't even red over the local catalog! In this oak, I know only one bed for a pony, and that bed is mine."
Her vis-a-vis gave her a sly smile.
"Since my very arrival from Canterlot," Twilight started venomously, "lots of ponies have been trying to make friends with me; but none of them has tried to get into my bed."
Nightmare blinked a couple times, with mouth agape, then raised her hoof to her forehead with feeling; the hoof-shell clanged loudly against the metal of her helmet.
"What does it have to do with you! I've dreamed of a bed for a pony for the whole millennium, a bed with starched linen and fluffy pillows. If anypony has anything against that, they can kiss my cutie mark!
The mare took a running jump and plopped down on the bed, pleased with herself; though that very instant four hooves pressed against her side, and, caught off guard, the tyrantess clattered over the edge.
"Take off the iron…"
Nightmare's desire was getting irresistible, so she removed her armor without a word, immediately attacked by pieces of cloth that turned out to be a suitably sized black pajama decorated with stars.
Having got through that, she found Twilight climbing into a pajama bearing a floral ornament.
Finally they both settled down.
The cover rustled towards the black mare.
"Oh Celestia!"
"Don't dare mentiommmphuh!"
A pillow flew away from the alicorna's face as fast as it arrived.
"O Mighty Nightmare Moon," irritated, Twilight levitated another cover over to herself, "bless the subsequent eight hours of eternal night for sleep."
"Amen."
Her brain didn't make her ask twice, and fell into a deep sleep without dreams.
Awaking, Twilight opened her eyes… and her sight got filled with blackness. Her nose was pressing to it, and it was material, and smelled pony. A little farther a nebulous mane was fluctuating.
Nightmare Moon.
Well, bodies without brains turned out to be more cooperative than bodies with brains.
Now that she wasn't starved of sleep, Twilight felt no antipathy she'd felt to the mare the day before. Nothing irreparable had been done, and, regarding her story, she merited compassion and help.
Having gently pulled away from the guest, Twilight ignited her horn; outside the window, a sky blue sphere with bright yellow core swelled, fairly plausibly imitating diffuse sunlight. The "sun's" rays started to move toward the bed, scaled the sheet, warmed the velvet of the black cheek…
"Aaaah!!! No! Impossible!" The mare rolled off the bed and recoiled to the wall, trying to get into fighting stance.
Satisfied, Twilight quenched the sphere.
"Funny," she remarked friendly, "it's bothering you more than the absence of your pajama."
Caught unawares a second time, Nightmare gripped her belly, but her hooves found the cloth in place, as should've been expected. Tail down, she stumbled to the bed and perched on its edge.
"I am not prepared to fight you, Twilight Sparkle. Pillows, coffee, pajamas… No, a thousand years ago everything was different."
Twilight touched the crescent reassuringly.
"You know, maybe our introduction was a little extreme, but… Since my arrival to Ponyville I've been showered with new acquaintances; but nobody I've come to know as well as I know you now."
Her interlocutrix's hoof lay over her own.
"You are not a bad pony. Why wouldn't we rule together? I won't feel that lonely, and you will gain the same power as I."
"I have a proposition too, and I'd like you to accept it," Twilight threw the second hoof and pulled the Mare from the Moon closer. "We'll leave the country under the same wing it is now, while putting more focus on our friendship. I have this research in my program, we can have as much time together as you like. And later, maybe, we'll get to geopolitics."
Nightmare slowly lowered her body, stretching and relaxing her limbs. Can friendship of one pony be worth more than the whole Equestria? As tension was leaving muscles, a magical thread feeding a seal applied in an appropriate place was fading out; Nightmare allowed it to disappear.
Light came through closed eyelids: the sun was rising over Equestria. Four clops came from the window's direction — Princess Celestia condensed from sunshine, setting a hoof on the wood of the floor.
"I counted on you, my faithful student," the princess fixed sunglasses at her forehead.
"Not even leaving home," boasted Twilight, and they hoof-bumped, pleased with themselves.
"Hello again, Nightmare Moon," Celestia cheerfully hugged the frowned pony. "Or should I say—Luna?"
"Let's start with a 'sister'."
"Wonderful. Twilight, five ponies are approaching the library. I think we'd better meet them downstairs."
The three of them descended to the main hall.
"It was not how I had imagined my return, Twilight Sparkle," Nightmare-Luna confessed, "but I think it was to the good. I hope to succeed in earning the sympathy of our little ponies in a different way. And regarding one very special pony… I would like to become your friend. You know much, and you see things that others do not. And I could teach you something other than dethroning relatives."
"Especially since that's not your forte," Celestia chopped in. Her sister gave her a displeased look, then grinned at some thought predatorily.
"The proposal is accepted," Twilight replied with a smile, and her mentor beamed even brighter.
"Wonderful! Herewith I pronounce you student and... student."
The moon pony shuffled her wings hesitantly; the unicorna stepped towards her encouragingly, and sunk into rustling of black feathers, becoming the first pony receiving such a gesture in a thousand years. Seconds later the sound repeated—that was Celestia embracing them both, so now it was two princesses lowering their heads to the little unicorna.
"This day's events may appear trivial, Twilight, such a fortunate outcome they have; but in fact, what you have accomplished is a feat. I am so grateful to you—Luna and I can finally have a talk, without wasting time on sweeping our horns.
"I'm glad everything's got resolved, but I think it's not a good time to relax. What can ponies think when they see us like this?"
"We'll find an explanation for them."
"What I can think?"
A bit too quickly, the sisters got on their hooves, taking a short step from Twilight. Looking at the ceiling, Celestia proclaimed, her voice trembling once:
"I have no doubt that you will analyze everything and reveal the truth."
"Okay, let's save it for later. The only question remains: what are we going to say to all the ponies who have attended the yesterday ceremony?"
"Well, if the old methods are still in use…" Nightmare-Luna created a pair of sunglasses and put them on Twilight and herself, "we'll tell them it was swamp gas."
