My eyes snap open at the sound of something hitting the floor; the loud, awful crunching of what I'm guessing to be a piece of expensive, pre-Classical era pottery seems to reverberate around the entire palace … at least, that's how it feels to me in my half-awake state. Only for a moment does the decadent notion of ignoring it, turning over and trying to get back to sleep flit through my mind. It's almost time for my daily ritual, anyway, and I show my commitment to the getting-up process by telekinetically hurling the covers off of my body. Instantly, the cold air causes goosebumps to rise along my flesh and I wonder what the point of my thick, alabaster pelt is exactly.

The bed is big enough to comfortably house three or four me-sized ponies, and as I lazily wash my puffy, bleary-eyed face in the en-suite, I imagine the scandalous articles that would be printed should something of that nature ever be allowed to occur. Certainly, it would liven up an otherwise dull period for news. I shake my head, dimly aware that I'm  sending droplets of water cascading everywhere; I haven't found the time to go on one date in several hundred years, never mind the logistical nightmare it would be to find three or four willing participants …

I suppose it's pretty obvious by now that I'm trying to distract myself with this pointless minutiae, trying to ignore the fact that further noises have been tumbling out of the suite a few doors down from my chambers; her first day back was, to say the least, trying, and the information overload – dozens of unfamiliar ponies around the castle to meet, getting used to a whole new language and set of customs, even the plethora of strange foods on offer – had exhausted her both mentally and physically to the extent that she'd been asleep for almost sixteen hours now.

For someone so used to having all the answers, I'm unsure as to what the right thing to do here is; do I allow her the space and time she most likely needs, or do I coddle her, keep her close, and find some way to bridge that thousand-year-chasm that keeps us separated? I've learned patience over the past millennium, but all I want to do right now is hold my sister close and not let her go ever again.

A smile blossoms and withers on my face as yet another object collides with the wall; Twilight Sparkle, were she here, would no doubt be babbling a library's worth of psychology textbooks at me right now about sibling relationships and the like. The thought briefly crosses my mind of summoning her for assistance – at the very least, it would be somepony I could talk to as something akin to an equal – but it wouldn't be fair to drag her from her new friends, her new life, in Ponyville to listen to my domestic problems.

Exiting my room, I greet the two guards who stand constant vigil over me. It's clear from the tightness in their faces that they've heard the commotion coming from Luna's suite, too, but are unsure what to do about it; no doubt, they've been patiently awaiting my presence in the hopes that I'll be able to set things to rights. “She said she wanted to be left alone,” one of them calls to me as I make my way down the hall, “though we don't know whether she was including you in that ban or not.”

Standing in front of the polished oak door, I am hesitant to knock. One can imagine the need to blow off some steam after such a long imprisonment, and maybe I'm worrying over nothing. My way of coping with stress involves soapy bubbles and a crack team of masseuses who can do things to your body that should only be possible at the hooves of a dedicated lover, but there are others who prefer more physical pursuits to burn off their stockpiled aggression.

Politely, almost timidly, I bring a hoof to the door; the knock is so tiny, so delicate, that even I'm having trouble hearing it. Instantly, all activity from Luna's room ceases. I should be relieved at the cessation of whatever hostilities she was enacting against the décor, but I'm not. The silence is so absolute that it weighs on my mind until a single, choked sob brings me back to my senses and I decide to banish any sense of royal decorum to Tartarus as I shoulder-barge the door open, practically tearing it off its hinges in the process.

Very few things in life can shake me to my core; I've lived a long time now, so long that even I have trouble remembering where and when it all began, and I've experienced just about everything that an organic being is capable of … all that said, the sight before me was so unnerving that I was grateful not to have had breakfast yet. My empty stomach settled for knotting itself uneasily, sending a cold shiver up my spine, sweat forming on my brow.

The decorators had done a truly sterling job matching Luna's new suite to her original one from our old palace in the Everfree Forest; right down to the patterning on the frame of the clerestory through which one could observe Equestria in all its majesty, the details were perfect.

Well, no longer.

The state the room was in you'd think that it had played host to a party of stampeding Minotaurs. It was difficult to believe that the fragile, crying pony sitting in the midst of all this chaos, wings wrapped around her like a blanket, was responsible for the cracks spider-webbing the marble walls, the shelves disgorged of their contents, the smashed windows, and the pages torn from books still fluttering to the ground like dead leaves falling from a withered tree. I'm amazed that she didn't hurt herself in the process of causing so much devastation.

So focused am I on my blubbering younger sister – she looks so childlike and helpless, with snot and tears streaming down her face with abandon, that I can't think of a more appropriate word, undignified as it is – that it takes my eyes a moment to register something alarming: the cracks, when I tilt my head to the proper angle, are resolving themselves into words. In fact, a whole sentence has been painstakingly etched into the marmoreal. It takes me a couple of spins until I fully digest what the walls are trying to tell me.

YOU WILL NEVER BE FREE OF ME, AWILIX.

My blood runs cold. In the whole history of Equestria, only five ponies knew that Celestia and Luna were not our true, birth-given names; ourselves, obviously, while another two of them, our parents, have long since passed on to the next plane of existence. Leaving …

The fifth.

Luna's wings quivered slightly in agitation, allowing me my first proper look at her face. She appeared wretched and miserable, and I can't blame her. Any honeyed words of comfort that might've tumbled unthinkingly out of my mouth have long since deserted me as I take in the horror around me once more; we thought ourselves free of this millennium-long nightmare, finally, that the Elements of Harmony had destroyed the dark presence that had allowed the very worst aspects of her psyche free reign over her body.

I suppress a shudder; I have no desire to relive those days in my memory, no wish to revisit the terrible things Luna was forced to do.

Forced?

Am I trying to let her off the hook too much? The one question I've always wanted an answer to, yet have been too afraid to ask her since her return: how much of it was you and how much of it was Nightmare Moon? My sister's jealousy of my role as the Princess of the Sun played its part in pushing her over the edge, but without the poisonous influence of that demonic entity manipulating her … I don't know. I don't think I want to know. It's easier to believe that my dear, sweet sister was the innocent victim of a higher power's meddling.

It makes it easier to love her as I once did.

Luna's eyes open suddenly; if I didn't know any better, I could almost have believed that she was waking up from a brief slumber. She blinks a couple of times in confusion, as if unable to comprehend the fracas surrounding her. “Celestia?” she says in the low, shaky voice of a child faced with something they cannot understand and looking to an elder for succour. It suddenly occurs to me that she was still practically a child when I was forced to exile her. “What happened? What did … what did I do?” A child who had to learn the hard way that adults don't always have the answers that they need.

“What's the last thing you remember?” I ask quietly.

“I was exhausted from the impromptu homecoming celebration and I retired to bed. When I awoke, it was to all of this.” She punctuated the final word with a sweeping gesture that took in the whole, demolished suite. Her tone became fearful. “It's back, isn't it? The Elements-”

“They failed to purge completely the Nightmare's lingering essence from your body, it seems,” I replied, trying to keep my voice level for Luna's sake. She was already scared out of her mind and it wouldn't help if I were to also lose my cool. My sister was counting on me to be a bulwark against the insanity within her.

“I knew this would happen,” Luna says so softly I almost didn't hear, even though I was sitting right next to her. Her head slumped forward and her breathing was coming in ragged gasps. She wanted to run from this, to flee to some place it could never catch her, but there was nowhere far enough out of its reach ...

My wings extend to their full length and reach out to the smaller pony, pulling her in close. “Knew what?”

Luna's head rests against my chest; no doubt my rapid heartbeat betrays the tension I'm feeling, but she doesn't mention this. In a strange way, I think it comforts her, the reminder that I am just as much flesh and blood as she is. “That I wouldn't escape the Nightmare, not permanently. I was hoping for a bit more time, though. Time enough to make amends to the ponies of Equestria. Time enough to apologise for every hateful thing I ever did to you.” Fresh rivers of tears fall, soaking my coat.

“Sh,” I say, using the same cooing voice that brought so much comfort to us as fillies when whispered by our parents. My wing-grip on her tightens; I use a hoof to brush her flowing, ethereal mane back, bring my muzzle level with her now-exposed ear and hum an old lullaby that they once sang us to sleep with. It takes a few moments, but soon the melody has the desired effect in lowering both our heartbeats to something like their normal speed. Luna's withers visibly slumped as the stress oozed from her somewhat. “Better?”

“A little.” Luna looks up at me, her eyes so filled with unconditional love and absolute faith in me that I feel my composure beginning to slip once more. For just a moment, I'm not seeing my sister, but the bright, inquisitive gaze of Twilight Sparkle instead: naïve, innocent, trusting. Expecting me to have a solution for every problem, no matter how insurmountable. “What can we do?” She hesitates, frowning. “Is there anything we can do to stop it?”

“Honestly, I'm not sure,” I admit, and it hurts me to be so clueless with my sister's soul on the line. “There was a small risk that a part of the Nightmare entity might survive the Elements of Harmony's assault, but I had no way of knowing for certain until you were actually exposed to their power.” I look directly into Luna's eyes, my voice dropping an octave. “What I do know is that it is a magical parasite and it will grow in strength the longer we leave it, until you … succumb once more to its will.”

“Then, we have but one option open to us, dear sister.”

“Wha-?” I begin before I realise what she's referring to. “No, absolutely not. Never again.”

A soft sigh escapes Luna and she speaks to me resolutely. “I have no desire to become that despicable fiend again.”

“It may not happen.”

“Look around you. It already is happening. At the moment, it can only exert control over me when I'm sleeping, but once its power grows there'll be no stopping it.”

“Luna, I am not banishing you to the Moon once more. It was torture enough to do it when the Nightmare entity had full control of you. A second time, when there's still hope of a better outcome, would kill me,” I say angrily, considering the matter now closed. “We will find another solution.”

“There isn't one. Celestia, dear sister, look at me.”

Reluctantly, I do so. I don't see the Princess of the Night, or a powerful alicorn, I just see my baby sister in need of a helping hoof.

“I do not want to become Nightmare Moon again,” she says sternly, and I realise from her ominous mien that she is deadly serious about doing whatever it takes to prevent that loathsome being from arising once more within her. Her voice turns soft. “Exile, one day after returning, is far from what I wanted, dear sister, but a taste of freedom is better than nothing at all. And in another thousand years, you can try vanquishing the entity with the Elements of Harmony again.”

“Or maybe I can just ask it nicely to leave,” I reply, trying – badly – to lighten the mood. One day is not enough time. How could the deities that watch over us be so cruel as to return my sister to me only to immediately snatch her away? Is this some sort of divine punishment? What could I have done that was so awful that they see fit to chastise me in such a harsh manner?

“Maybe you could,” says Luna. It takes me a moment to realise that she isn't kidding either.

“What do you mean?”

“I know your control of the Tjukurpa is imperfect since you were never meant to wield it, but you've managed for a thousand years and I know you'll be able to do this. Enter my mind, find the personification of the Nightmare within my dreamscape, and ...”

“And what?” I ask in a strangled whisper. “Attempt to reason with it? Negotiate with something that simply wants power and glory for its own sake?”

“Yes,” replies Luna bluntly. Off my look, she adds: “You wanted another option and this is it. If it doesn't work, you can then banish me to the Moon secure in the knowledge that you tried everything.”

I'm about to respond when I discern the rebuke contained in her words and I'm left momentarily smarting. “You feel that I was too hasty when I sent you to the Moon before?” I suppose I should've been angry at my sister's accusation, but I wasn't; I've regretted my decision every day, but I knew in my heart – as I know now – that I did what I did because there was no better option available to me. I tried reason once, and all it got me was a ruined castle and a battle with the one pony that mattered most to me in the world.

Luna disentangled herself from my wings and shifted to a more comfortable sitting position facing me; her horn is tantalisingly close to my own, but they are not yet touching. It's a tremendously intimate act, though few know the true significance of why that is: when two unicorn or alicorn horns are brought into contact, a spark of their residual magical essence is released. It flows from one into the other, becoming a part of them. In some ancient cultures, it was used as a form of ritual bonding in foalhood; to others, it was simply a way of showing affection to a loved one. “Are you ready, dear sister?”

“No,” I reply truthfully.

“One never knows what evil they'll find lurking in a pony's heart,” she says with the slightest of smiles on her lips.

“You're not evil,” I say to her. They are the last words I am able to utter before our horns collide with a sharp clack and the flow of dream-shaping magic makes Luna, the room, everything, go swimmy and disjointed.

I'm disappointed, though I shouldn't have been terribly surprised, to find that the inside of Luna's head resembles the suite that our real-world bodies are currently occupying. You tend to bring with you your own preconceptions, and while the dreamscape could conceivably take on any form, I prefer for it to look like something safe and familiar. Probably the reason why I was never very good at utilising this remarkable power. Equestria definitely suffered in that regard during Luna's absence.

Many more years ago now than I can comfortably recall, we were schooled in the various aspects of magic by our tutors. Luna particularly excelled at Tjukurpa: the art and science of dreaming. Coupled with her natural affinity for astronomy and astrology, she was the perfect choice to be elevated to the Princess of the Night, the Protector of Dreams. Maybe things would've been different if she knew how much I envied her devotion to her craft? All I do is hurl a giant flaming ball of gas into the sky. My sister meticulously arranges the heavens themselves.

Unlike Luna's room in reality, this one has a cold, distinctly unwelcoming, cast to it; the outer edges are well-lit, and I can see many of the familiar objects that decorate it, but they're all curiously lifeless, as if they've been robbed of their vivacity: paintings, bits of pottery, a few knick-knacks collected or inherited over the years, all of them grey and dull. Toward the centre, however, the light begins to fade away until the middle of the room is in complete blackness. It's not just an absence of illumination, it's an absence of anything. A void.

A sliver of moonlight peeks in through the high window, striking the core of the black mass. It reacts as if struck and begins to recoil; snake-like tendrils lash out from the retreating blob in every direction, searching for the source of the intrusion, and I'm forced to retreat behind Luna's unmade bed to avoid being caught in their web. After a moment or two passes, I risk a look and see that the blackness is beginning to take on a very familiar shape. At first, I think it is my sister. In a way, I suppose it is.

Once more, Nightmare Moon stands before me. Jet black in colour, glistening fangs in search of something to bite down on peer out over her lips, clad in an approximation of ancient Equestrian battle armour … I wonder if it's my subconscious impressions or some act of the dreamscape that gives her an additional layer of menace. Or is it because she's weak? When backed into a corner, there is nothing that a living being won't do in order to survive.

She, it – whatever – moves, but not toward me; long, ebony wings unfurl and carry Nightmare Moon gracefully into the air. She alights on a plinth overlooking the clerestory. From her demeanour, I get the impression that she is waiting for me to follow her. Even without the borrowed alicorn form, I have trouble thinking of the creature as anything other than female. She has a predatory air about her and the best hunters are generally female.

“Princess,” she says to me as I land gently across from her; her intonation makes it sound like a curse, though I could just be imagining that. She turns away from me and gazes out of the window, admiring the vista of Moon and stars. Even the blood-red swirl of the Horsehead Nebula is visible to the naked eye. “Beautiful, isn't it?”

“Yes, it is.” I try to keep my tone neutral, but it's difficult not to be moved by such beauty, even if it is only a dream. It serves as a dramatic example of what Luna is capable of.

“A work of art remade every night, and what thanks did I, did we, ever get for it? Eternal ignorance.” She bares her fangs at me in a cruel smile. “I know why you're here, and I want you to know why it's pointless. Even if I hadn't been there to give her a much-needed little push, Luna would've snapped on her own eventually. She's a terribly broken pony, you know? Consumed with jealousy and bitterness that her efforts continually go unnoticed. The only thing that stops her from acting and claiming her rightful glory is you. More specifically, her love for you. But that isn't going to restrain her forever.”

“You're wrong,” I replied simply. It was amazing the level of clarity I felt at this moment. So many villains had tried and failed to conquer Equestria. Discord, Tirek, King Sombra … but none of them had ever succeeded in doing what Nightmare Moon had accomplished: driving a wedge between me and my sister.

Nightmare Moon bristled at my words. “What do you mean?”

“Luna is the strongest pony I've ever known. Yes, she made a mistake once, but that's in the past. To come back seeking forgiveness, to attempt to rebuild her life in what is tantamount to a whole new world for her, shows the depth of her character. If you hadn't been whispering your poison in her ear, she would've come to me and we would've found a way to resolve things without the need for fighting … or the need to banish her for a thousand years. This was all your doing and I was a fool if I ever thought it otherwise.”

For a moment, Nightmare Moon looked angry, but then her features softened until she was almost smiling. “Well, you can't blame me for trying.”

Before she'd even finished speaking, her horn ignited with energy and I barely had time to duck under the howling bolt of green lightning sent my way; the column behind me shattered into a thousand pieces of smoking rubble, most of them seeing fit to hurl themselves in my direction until I was peppered with tiny cuts. I got to my hooves and fired back a volley of my own. It was much too slow and Nightmare Moon easily deflected it, sending the surge back toward where I was still brushing the dust and debris from my coat. It caught me square on the chest and I staggered backwards, a grunt of pain escaping my lips as I collapsed in a heap.

“If that's the best you can do, you might as well surrender to me now, Princess,” she said, practically purring the words as she thought her victory certain. She'd had a thousand years inside Luna's head; she knew the rules of the dreamscape better than I did, and more than that she was incredibly, incredibly angry. “This is my domain. In here, I am the Goddess.”

“No, you're not,” a new but very familiar voice said, echoing through the carnage in the room.

Nightmare Moon paused a split-second before delivering what probably would've been a fatal blow to me. She looked around confusedly for the source. “Who ...? Where ...?”

I looked up through my pain to see Luna. Her eyes were blazing with an incandescent light. “This is my realm. This is my mind. And I will share it with you no longer.” My sister's body seemed to be burning with a white-hot glow, as if she were pouring her entire soul into her attack. Nightmare Moon had nowhere to run as her whole being was engulfed by the wild beam of energy coruscating from Luna. After one last jarring wail that hurt my ears to hear, she was finally gone.

Luna joined me on the plinth, extending a hoof to help me up. “Thank you,” she said, throwing her forelegs around my neck.

“For what?” I ask.

“For what you said. I've been afraid all this time that you wouldn't be able to separate my actions from those of the monster, and that we would never be able to go back to the way things were. I ...” she trailed off, looking embarrassed, “I'm sorry for ever having doubted you, Celestia.”

“Dear sister, many things in this world will change, but not my feelings for you,” I say, returning the embrace. “I should be apologising to you for ever having thought that you could be complicit in the actions of Nightmare Moon.”

“Then,” she shoots me a faint smile, “you are not afraid that I will one day snap and attempt to usurp your throne?”

“No.” I'm amazed at how light I suddenly feel after uttering that simple word. Nightmare Moon wanted to divide us once more, to weaken Luna to the point where she would accept its disgusting influence again, but it failed because of my sister's strength. She is not the same pony she was a thousand years ago. During those long, miserable days alone, she has learned wisdom.

We extricate ourselves from the hug and spend a few moments in quiet contemplation. The Nightmare entity has been vanquished, but who is to say that it is the only one of its kind? Perhaps there are others like it out there, poised to strike at the moment any pony feels weak or rejected. I say as much to Luna.

“It doesn't matter,” she replies, placing a comforting hoof on my shoulder. “Together, we will stand against any darkness.”