“Princess Luna. It has been a thousand years since I’ve seen you like this.” – Princess Celestia.

It started with a crunch.

Pebbles rolled down the cave’s dark insides, clattering downwards in a miniature avalanche. Light, ghostly and white, flickered in an uncertain circle from where the rocks had fallen, a blocked tunnel at the tip of an intestinal track that wound deep into the cave's depths. There was another crunch, and then a rumble as the circle grew thicker, and the light pouring through became brighter.

And then the shadow at its centre moved to one side, so that the light looked like a waxing crescent moon. And when that light was full and round, a figure could be made out at its centre, horn ablaze as she shifted the boulder covering the cave roughly to one side. There was a boom as the rock was dropped; the light from her forehead went out, but the light pouring off the rest of her shone on.

Princess Celestia entered through the hole she’d made, her hoofsteps fast and certain. The cave’s sides lit up around her as she passed without stopping or looking around; divergences and splits inside the tunnel’s wanderings were overcome without pause or even a spared glance towards the other passages.

The grey rock that was the cave’s sides gleamed at her as she strode past them, faint traces of ice and embedded crystals glinting at her from time to time. Occasional scrabbles of things inside the rocks whispered out as the light flowing from out of her hair danced off the broken pillars and buildings of ancient ruins submerged into the rock.

Eventually, and without much warning, she stopped. The light surrounding her increased, flooding forwards to shine and glimmer off of a golden door embedded into the grey stone of the cave. A door that was on the ceiling.

Celestia paced towards it, neck craning backwards as she examined the door. She stopped when she was underneath it, face no longer a mask of indifference, but one with fixated eyes and short, almost-panting breaths. Her eyes closed over, and she shook her head once, before lowering it. She sighed out, her breathing now controlled.

Her wings almost touched the tunnel’s sides as they stretched out. And then, with one powerful downbeat that disturbed no air, she rose up, horn pointed towards a hole in the door’s centre. Another wingbeat, and it slid carefully in. The door cracked open, and Celestia fell through, gravity suddenly reversing and pulling her inside.

Then, as she entered, the door slammed firmly shut behind her; gravity, apparently fickle, threw her onto it.

“As charming and as graceful an entrance as I’d expect, Celestia.” The voice was female, dark and vicious. Celestia’s head turned to her left, eyes meeting those of a tall, black pony, legs separated and bound onto the wall by purple, humming chains. She smirked.

“Though I must admit that it at least gives me something to look forward to. Two centuries you’ve been using that entrance, and every time you end up crumpled on the floor.” She laughed. “Oh, you never learn, Celestia.”

“It’s good to see you, Luna.” Celestia rose back onto her feet, wings tucking back into her sides and the slight grey stains of dust vanishing from her sides. “Or Nightmare Moon. I forget which one you prefer to be called by.”

“Either will do. I have no real interest in what you call me by.” Nightmare Moon watched as Celestia walked towards her, the sound of her hooves loud inside the small, orb-like cavern that was beyond the gold door. “So... What are we to talk about this time, hmm? Will you be asking me why again? Oh, why gets so boring. Perhaps you’ll ask me how this time.” Her head leaned forwards as far as the chains slack would let it. “Or perhaps we’ll try and flesh it out through babbling nonsenses first of all.”

Celestia’s head tilted towards one side, her expression impassive and unreadable. Her lips remained shut.

“Or perhaps you’ll say nothing and just stare at me for the entire time.” Nightmare Moon snorted, and her head snaked back. “Fine, Celestia. Why?”

Immediately, “You gave me no choice.” Celestia gave no sign that she had spoken.

“No choice? I told you to step aside.”

“You would have shattered harmony, disrupted everything we managed to salvage from Discord.”

“And? It was ours to break; we made it, forged it, kept it strong. It was by our diligence that harmony was preserved, and by our suffering that it was birthed. Or have you forgotten the Elysian Fields?”

“That does not mean we had the right!” Celestia took a step towards her sister. “We never created it, Luna; we only found what they had lost.”

“Then perhaps they could have learned diligence too.” Nightmare Moon chuckled, head lolling back as her eyes combed the ceiling. “Oh, come Celestia. We both know where this is going. You chose them over me.”

Celestia’s lips pursed together, and she blinked slowly. The grin faded from Nightmare Moon’s face.

“You chose them over me,” Nightmare Moon spat. Sparks foamed from out her mane to splatter uselessly against the chains wrapped around her. “That’s what it comes down to, in the end. I asked you to choose, and you choose them. Over your own sister.” Celestia’s eyes had closed over; a slight frown hung over them. “You can try and pretend that what you did was right, that you still love me, but –”

“I wasn’t enough!”

Dust slid off the cavern’s sides in hazy waterfalls as the shout echoed and echoed, getting louder instead of quieter. Celestia’s eyes were red and open and locked onto Nightmare Moon’s.

“I begged with you to listen, Luna. Begged. I loved your nights and I loved you, but my love was not enough. I never gave up on you, Luna; I waited until there was nothing left that I could do. No. I didn’t choose them. You did. My love alone was not enough for you; you wanted theirs. You wanted it more than you wanted mine.”

Nightmare Moon’s green eyes were wide and staring. And then they crinkled, and the corners of her lips turned up. And then she laughed.

“Ha ha ha ha-hah... Oh, don’t yo- Don’t you see?” Nightmare’s head snapped back, tears pouring down her cheeks as she cried with laughter. “We both... We both chose them! Heh heh heh heh heh. W-We were given the choice, and – ha hah ha – and we didn’t choose each other. Ha, ha hah.” Her head flopped back down and she gasped out a few wheezing breaths. “The... The only difference is that they... they chose you.” She giggled again. “And we have this conversation every time, don’t we? Every single time, always the same. You truly never learn.”

Celestia breathed out, and it was a long, drawn out thing. She turned, walking back towards the golden outline of the door, carved into the floor like a mosaic. Her front hoof had just collided heavily with it when a louder sound interrupted her hoofsteps.

“Celestia? Sis- Sister?” Celestia stopped and turned; Nightmare Moon had stopped laughing, though Luna’s eyes were still wet. “When will you return?”

“There’s a problem with the Griffon Kingdom; it may be a while before I can visit again. Dealing with the diplomats alone may keep me more than a month this time. I’ll be back as soon as I can.”

There was no response. Celestia left.