The dungeon remained empty most of the time. Incarcerating a pony rarely happened anymore; Canterlot Castle only had a dungeon as a relic of past times. The custodial staff maintained everything, of course. No cobwebs or dust adorned the corners, no spiders or rats prowled the walls. Yet the air still smelt stale, the cold still clawed at Celestia’s coat. Even a sun goddess couldn’t keep away such a permeating chill.
She stepped through a few doors. No guards stood watch or accompanied her. Cadance had offered to come along, but Celestia had declined. Finally she arrived at the cell farthest from the entrance.
“Hello, sister,” she said simply.
“Hello, Celestia,” Luna replied. She did not turn from the wall. “I assume you know what I did, by now.”
“They are still cleaning up the remains, but yes, I am aware.” Celestia glanced around the cell Luna had chosen. It looked as empty as all the others. “We could be having this conversation in a more comfortable room, you know. You don’t need to embellish your explanations with theatrics.”
“I wanted to remind myself of something, of how it feels with no wind and no sun.”
Celestia sat down. The cold clawed at her again. Even with the power of the sun radiating from her, the stone tiles felt like ice. The architect had probably enchanted them to do that. “Why did you do it?”
“I was scared. Scared of what might happen if he won.”
“We were all scared, Luna! That didn’t give you the right to take his life!”
Luna finally turned away from the wall. “Hiding would not have worked. He would have found Twilight eventually. And she would not have been able to control our magic, not even a little.”
Celestia watched Luna carefully. Something about her body language seemed off. “There is something you aren’t telling me, Luna. Simple fear doesn’t explain such a heinous action.”
“I’ve had to live in a dead world, Celestia. The thought of it scares me more than you could imagine.”
Celestia opened her mouth, but paused. “I…I did not think that your time on the moon had affected you so strongly.” She tried to hide the guilt from her voice, but it leaked out regardless.
“No, that is not what I meant. I…” Luna sighed, turned back to the wall. “There is something I have needed to tell you, Celestia, ever since I came back from the moon.”
She rose, and turned her body to face Celestia. Her gaze still lingered on dungeon walls. “What…what would you say if I wasn’t the Luna you knew?”
Celestia bit her lip. “Luna, I know that your time on the moon changed you. More than I thought, given this—”
“No, it is more complicated than that.” Luna sighed. “A long time ago, very long, I…” Luna tore her gaze from the dungeon wall, made eye contact with Celestia. “Perhaps I could show you, that would be simpler.”
“Show me wh—”
Before Celestia could finish, light began to leak off Luna’s body. Her horn didn’t ignite, so no spell was being cast. Lines of blue magic spiderwebbed across her coat, and they grew thicker and brighter as more appeared. Luna closed her eyes, took a deep breath. Her coat began to flake off, like paint peeling off an old building. Bigger chunks began to peel away, and black hair poked out of the holes. The fallen bits hit the floor and evaporated.
Luna took another breath, and blue light flooded the room.
Celestia uncovered her eyes. She tried to say something, but she found no words.
Luna stood in front her, but it wasn’t Luna. She looked like Nightmare Moon, tall and sleek. Yet her armor was absent, her fangs were missing, her eyes and pupils retained their normal color and shape.
“Luna, this…this is not funny.”
Luna sat down. Her eyes were now level with Celestia’s. “This is my true form, Celestia. I would never joke about something like this.”
“I do not understand,” Celestia said. It had been a long time since she had last said that, but the situation warranted it.
Luna took another breath and smiled. “It feels so nice, not having to wear that. I didn’t realize how cramped it had become,” she said. Celestia caught a glimpse of her canines, worn flat instead of pointed and ridged.
The smile faded. “It all happened such a long time ago,” Luna said. “Nightmare Moon whispered so many sweet lies to me, told me how poisonous and destructive you were.”
Celestia said nothing. Luna had never spoken about this so openly before. The sudden candidness unsettled her as much as the words themselves.
“I tried to ignore her, at first. I wanted to be loyal to my sister. But it didn’t last. Seeing all those ponies enjoying the day so much and sleeping through the night, it made Nightmare Moon’s claims so hard to write off.”
“She made me so many promises, Celestia.” Luna closed her eyes, and the edges started to glisten. “She kept telling me how much better things could be, how much respect and adoration I could get, if I only did one thing.”
Luna opened her eyes, slowly. She bit her lip, and tears ran down her cheeks. “So one day, I gave in. I was weak and I gave in. And…” Luna moved her head, tried to look at Celestia and failed. “And I killed you.”
“I don’t think you did, sister.”
“No, no that’s not all.” Luna looked up at Celestia. “Once you were dead, I got rid of the sun. I made everypony build me a new castle, I kept listening to Nightmare Moon, all the whispered promises and lies.
“And eventually, everypony was dead. They couldn’t live without the sun, after all.”
“You’ve made your point, Luna,” Celestia whispered.
“And eventually, Nightmare Moon stopped whispering to me. I was all alone in a dead world for a millennium.” Luna smiled again, and it looked even more forced than the last one. “I would have done anything to escape that, even ask Discord for help.”
“And what did Discord do?” Celestia asked.
“He told me that history was immutable, and I told him, made him send me back anyway.” Luna turned away again. Her tears had stopped, but her voice lowered. “He threw me backwards in time, to this time. And when I got here, Luna was waiting for me. Your Luna.”
“She was hysterical. Nightmare Moon had already gotten to her, poisoned her. I tried to reason with her, I— I tried so hard to reason with her, but she wouldn’t listen. She attacked me, and…”
Silence saturated the room. It matched the chill. The silence stretched on, and the cold mingled with and reinforced it.
Celestia stood up, teeth clenched, and the cold retreated slightly. “And what?”
“And I killed her. I put on this disguise, and then I went to confront you in the throne room. I had to act it out properly. We fought and I had to make sure it looked convincing—” Luna’s eyes widened as pressure hit her throat. Luna’s back slammed onto the ground, her mane rippled and her wings flared.
“You mean to tell me that you killed my sister?” Celestia hissed.
“I am your sister too, Celestia.” Luna coughed. “A different one, but I am. I had to kill her, she would’ve destroyed the entire world.”
Celestia leaned down. She held her hoof to Luna’s throat, tried not to push too hard, tempting as it was. “And it’s just that simple? You travel back in time and fix your mistake and everything simply works out?”
“I had to fix my mistake, somehow. I had to…had to try something.”
Celestia grit her teeth. “If you traveled back in time and killed yourself, then why are you still here?”
“I…I don’t know.”
“Perhaps there is nothing left of Luna in you.”
“T-that’s not true…”
“You never questioned the mechanics of your journey before now? You were content to kill Luna, but you couldn’t be bothered to question why that didn’t kill you too?”
“Of course I questioned it!” Luna pressed her face into the floor. “I had no other choice! I had to end all that suffering, prevent it somehow!”
Celestia stood up, released her grip. “I understand your response to Tirek, now. All those years alone, corrupted by Nightmare Moon, they turned you into a sociopath, a pony who uses murder for all her problems.”
Luna rolled onto her side. “I tried so many things, Celestia. I tore apart the libraries looking for a solution. I tried every time travel spell I could find, tried to convince my past self to change her course. But every time it would fail. I would return to the present with nothing but a new memory. Another delusion among my collection. I had to end it somehow, I had to.”
Celestia turned to the door. “It sounds like your memories are not the most reliable source of information.”
“I had to protect Equestria, sister! If killing myself was the cost to pay, then I would gladly pay it again.”
“If you killed yourself, why are you still here?” Celestia asked quietly.
Luna said nothing. Celestia left.