Celestia found herself in a dark passage. The air was hot, damp, and still, and the blackness was so thick it was almost palpable. She felt as though she could barely draw breath in this horrible place, and what little air she did manage to get smelled of wetness and decay. She lit her horn and looked around. The low-ceilinged, claustrophobic passage stretched off in both directions, as far as she could see. The rough-hewn stone walls were coated with nasty, slimy muck.
Celestia started to walk. She couldn't say how she knew, but she was absolutely sure she was looking for something of vital importance. She didn't strictly know that she was going the right way, even, but some primal instinct told her she was on the right track. Her throat felt thick, her mouth dry, but the only water to be found was a sickly trickle wetting the walls. Even if she were to come across some sort of stream or water hole, she didn't think she would drink anything she found here.
Sweat beaded on her forehead, and suddenly, with the same inexplicable certainty, the feeling came upon her that she was very close to the thing she sought. Celestia started to run, her hooves making a veritable racket on the floor of the passage. Her heart, before long, started pounding, the rush of blood filling her ears.
She kept running, and though the gut feeling that was driving her did not lessen, she began to doubt very seriously that she was making any progress. Each foot of the passage was very much like the one before it, with not even a change in the slope of the floor to distinguish them. A simple change in the air would have been welcome—even if it was for the worse—because at least it would have told her that she was getting somewhere.
In spite of this, she kept running. She couldn't say how long she ran. It might have been hours; it might have been days. She soon felt lulled into a kind of trance by the steady drum of her pulse and the rhythmic ringing of her hooves. She hoped this search would end soon, but she felt she could run forever, if she had to.
Then, all at once, she felt a change. The air, after being nothing but stuffy, felt more free, and smelled a little fresher. Celestia pushed herself a bit harder, sure this time she was seconds away from what she'd come here to find.
She plunged ahead, and the passage widened into a chamber. After the cramped passage, this room felt palatial; its dimensions were more than enough to envelope her throne room back at Canterlot Castle, with plenty of space left to spare. She also became aware that the light from her horn was no longer necessary, there being rows of flaming sconces on the wall. Celestia didn't stop to admire the scenery, however; she sprinted straight to the far side of the room, where she skidded to a stop.
She had come to a large, ornate dais, with an equally large and ornate throne set upon it. On the throne was none other than Nightmare Moon, her body spread out in a cocky pose. She had her hind legs propped up on what seemed at first glance to be a footstool. Celestia looked and saw that it wasn't a footstool. It was a cage. Inside it was Luna, cowering and crying, still her old self in body, but seemingly shrunk down to a whimpering foal. Celestia knew that this was the reason for the urgency of her search—she hadn't been looking for something, but somepony.
Nightmare Moon looked Celestia up and down, threw her head back, and laughed. The gloating, insane sound filled the room, seemed to fill Celestia's whole brain.
“Well,” Nightmare said, “if it isn't Celestia.”
At this Luna, who hadn't yet noticed her sister's arrival, started. She looked into Celestia's eyes and pleaded, “Help me.”
“Quiet!” Nightmare boomed. She delivered a swift kick to the cage, silencing Luna.
“Let her go!” Celestia boomed right back, filling her voice with all the royal authority she could muster. She wasn't going to show it, not now, but the sight of Luna in a cage had shaken her, badly.
Nightmare Moon laughed again, so loud and so long that Celestia started to fear for her own sanity. “You do not command me, foal!” she said.
“Watch me,” Celestia said, more defiance in her voice than her heart.
“You have no power!” Nightmare positively screamed, the sound of her lunacy ricocheting everywhere at once. “No power over me, and no power to save your pathetic little sister!”
“We shall see,” said Celestia. Without another word, she began channeling energy to her horn.
“Magic?” Nightmare let loose one more howl of laughter. “Magic? The Elements have abandoned you, and without them, you have no hope. The puny energy within your own body will never be enough to outmatch me. Foal!” She spat the last word like a snake spitting poison.
Celestia remained silent, focusing her mind on her horn. With so much of her strength going to her magic, she wasn't able to hold in the single tear that slipped down her cheek.
Nightmare Moon saw it instantly. “You know! You weep, because you know! You will soon be dead, and in time, Luna will be no more.”
Celestia's mind was shouting at her that it couldn't be true, that she still could defeat the Nightmare and save Luna. But a deep part of her didn't believe it. The Elements had moved to new bearers, and they were the only way she'd ever beaten Nightmare Moon. She was doomed. Luna was doomed. Equestria was—
Celestia let the spell fly before her thoughts could overtake her. The bolt of yellow-white light hit its mark. The spell disappeared right into Nightmare Moon's chest; it appeared that she hadn't even tried to dodge it.
Cries from Nightmare's throat filled the chamber. Celestia thought, not daring to believe it, that she was screaming in agony. She watched Nightmare's body writhing upon the throne, and knew that there was no way it could have been so easy.
Celestia took a step toward Luna's cage, and then she saw, with a leaden lump of dread filling her stomach, that Nightmare Moon wasn't doubled up with pain, but with mirth. The sounds rising from the wicked mare were laughs, not screams.
Nightmare Moon straightened up and fixed Celestia with a deadly stare. “Did I not tell you that you had no power? You see, you are as helpless as a newborn filly.”
Celestia felt her insides turn to ice. She'd poured all her strength into that spell. How had it failed? Was she really as weak as Nightmare would have her believe?
Celestia noticed the blue aura building around Nightmare's horn just a split second before the spell fired. She spread her wings and took off, trying to get out of the way.
She wasn't fast enough. The beam struck her like a speeding train, and all at once she felt every muscle in her body seize up. She fell out of the air onto the cold stone. Landing on her side, she felt a rib crack.
In another moment, Nightmare Moon was standing over her. “Did I not warn you? Did I not foresee how this would end?”
Celestia felt magic take hold of her body, and Nightmare turned her around so that Luna's cage was within her field of vision.
“I think a fitting punishment for such foalishness,” said Nightmare Moon, “will be to watch your sister die.” She punctuated the sentence with a giggle of glee, sounding for all the world like a filly with a new toy.
Celestia wanted to close her eyes, but they were as immobile as the rest of her. Luna flailed helplessly in her cage, throwing her body against the bars with such force that Celestia could feel the bruises on her own body. She wondered briefly why Luna didn't just magic herself out, but then she realized that Nightmare Moon would certainly have thought of that.
There was a sudden flash, and Celestia watched as it struck Luna square in the face. She would have screamed if she'd been able. Luna's body slumped to the floor of the cage, the force of the spell having broken her horn and scorched her mane.
Now Nightmare Moon was standing over her once again. She lifted Celestia in her magic so that they were staring face-to-face. “A lovely little show, wasn't it?”
Without warning, she slammed her hoof into Celestia's muzzle. Celestia felt her nose snap, and a flood of metallic blood filled her mouth.
“Don't worry,” Nightmare Moon went on, “you shall soon join her. I will not allow you the dignity of being killed by magic, however.”
With that, she lowered her face toward Celestia's. She bared her pointed teeth, and they gleamed savagely in the torchlight. For one absurd instant, Celestia thought that Nightmare Moon was going to kiss her. Then it became perfectly clear what was happening.
She's going for my throat, Celestia thought, as those teeth seemed to fill her whole vision. She's going for my throat my throat my throat somepony help my throat we're all doomed and Equestria will perish and all is lost and oh no please not my throat…
* * *
Celestia woke up in a bed soaked with sweat. She felt her heart somewhere in her throat (not my throat, an echo from her subconscious seemed to shout), and she couldn't quite get her breathing under control.
“Breathe easy, sister,” said a voice from the darkness. “'Twas only a dream.”
“Luna.”
“I am here.”
Celestia felt her sister's hoof come to rest on top of her own. She lay there for a moment, trying to zero in on the feel of Luna's hoof, trying to shut the horrific images of the dream out of her mind, trying anything to get her breathing to return to normal.
After what felt like a long time, she finally felt a bit better. Not well by any stretch, but good enough to try sitting up in bed. She swung her hind legs over the side and raised herself to a sitting position. She performed some quick magic to light the lamps, and saw Luna seated beside her bed. Luna's brow was furrowed, her mouth turned down.
“I have never known you to have that dream, sister,” she said.
Celestia swallowed. “Perhaps not, but it is an old one. It plagued me almost every night after… after you were banished, but I don't think I've had it since your return.”
“But its meaning is clear enough,” said Luna.
“I'm sure it is.”
They lapsed into silence for a while. Celestia used her magic to fill a water glass from the pitcher on her bedside table, and drank deeply. Her eyes kept darting back to Luna. Celestia wasn't sure what Luna was going to say next, or whether it would be something she wanted to hear.
At last, Luna spoke again. “It was not your fault, dear sister. I am truly sorry you ever felt the need to blame yourself for what happened to me, but it was not your fault.”
As Luna said this, Celestia felt herself suddenly on the brink of tears. “I know it wasn't my fault, Luna. I just...” She stopped short and sniffed, blinking rapidly. “I just… don't know why I wasn't strong enough to save you.”
Luna looked at the floor. “It had nothing to do with strength,” she said. “There was nothing you could have done.”
“But I should have—”
“No,” said Luna, still not looking up. “There was nothing you could have done, because it was I who chose to start down that dark path.
“There are shadowy places in all of us—after what I have seen guarding Equestria's dreams, I am sure everypony possesses them—but most choose not to stay in those places for very long. I was different. I began to seek them out willingly, began to relish the time I spent lingering there. What I did not see—did not allow myself to see—is that these dark places are home to monsters, and I made myself susceptible to continuing to return to their lairs.
“Eventually, one of the monsters caught me, and forced me to become one with it. After that, there was absolutely nothing to be done. I had doomed myself. These monsters are so used to the darkness, so adapted to thrive in it, that there comes a point when they won't permit you to see the light anymore. Any light—even if it is the sun, standing in the same room—just appears as more blackness.”
Celestia saw tears sliding down Luna's face. “Luna, I—”
“So there was nothing to be done to save me, because I couldn't see you. Now, I know you only did what was necessary, to protect our subjects from me, and me from myself. But at that time, I was blind to all of that.”
Luna looked back up at her. “This is a lesson I had to learn the hard way, Celestia. I don't wish to see you repeat the mistakes I made by torturing myself with the Tantabus. You must forgive yourself, because I have already forgiven you; and I have already forgiven you, because you did nothing wrong.”
Celestia nodded, dimly aware that she herself was now openly crying.
Luna moved closer and hugged her. “I am sorry, sister. I wish you had never felt the need to punish yourself for my mistake.”
In those last words, Celestia heard the echo of what she'd said to Luna, when she'd learned from Twilight Sparkle what had been happening with the Tantabus. That thought was soon gone, however, and it gave way to the pure warmth of her sister holding her. She hugged Luna back, and knew that even if it took several more millenia, they would eventually get back to the way they were. They would return to the way they used to be, before Nightmare Moon robbed them of a thousand years of love.
