Disclaimer for a, probably, overdone fanfiction concept.

Nightmare Moon paced. The sharp sand of the moon had long ago ceased hurting her, although it had first caused cuts in her hooves and on her legs. A century (or had it been more? She had lost count several decades ago) of cuts and healing had caused callouses strong enough to fend of the particles.

Her fury waxed and waned, allowing her to scheme when she was calm and test the bonds that kept her prisoner and to drown out the maddening quiet of space with the rushing of her blood when it was at it's peak.

And the sound of her weak former self buried in the far back of her mind. The wailing was grating on her nerves more than the silence.

That damnable filly! She cried and cried and howled as if trying to submerge all of her fears in tears and drown out the source of her pain with her cries. Nightmare Moon would scream at the pathetic excuse for a princess to shut her trap if only she would do anything in retaliation but wail louder.

Newborn foals cried less.

She could hear her now, weeping and whimpering the name of her traitorous older sister. Once more, in a probably futile attempt to cause her former self to cease the infernal racket, Nightmare Moon turned her rage onto the snivelling, miserable creature. "CEASE THAT HELLISH NOISE!" she roared. The sound didn't manifest physically, much to her annoyance, but bounced around inside her skull in an almost tangible way.

The silence was unexpected and felt like a slap of cold water on a too hot summer's day. Nightmare Moon sighed heavily, smiling slightly at her victory.

Then, with the force of a gale and the willpower to topple mountains: "GIVE ME BACK MY BODY, YOU THIEVING PARASITE!"

The outburst came as a greater shock than the silence had. If anyone knew how much strength the filly actually had, it was Nightmare Moon. Then again, maybe she had gone insane some decades back and Luna was dead and gone and this was an illusion screaming at her.

Either way, it was phenomenal to finally have somewhere to direct her anger.

"Oh, found some guts, did we, Luna?" she asked with vicious good cheer, drawing out the syllables of the name for good measure. "About time. A bit too late-"

"GET OUT OF MY BODY!" her former self interrupted rudely, the heat of her rage spreading through the body. "GET OUT AND NEVER RETURN!"

Nightmare Moon laughed. She hated to be interrupted, but no one knew Luna like she did, and nothing would get to her more than laughter and ridicule. "It's my body, not yours. I couldn't get out even if I wanted to!"

The force of Luna's hatred wasn't almost physical, it actually caused Nightmare Moon to stumble to her knees. "THEN CRAWL BACK TO WHATEVER CESSPOOL YOU EMERGED FROM, YOU PISSPOOR IMITATION OF A GODDESS!"

"Tsk, tsk, such language!" Nightmare Moon continued her tactic. "Besides, I can't! I'm you, remember?" she cooed the last bit.

The sudden disappearance of pressure that was Luna was yet another shock. Nightmare Moon had just resigned herself to the quiet when: "Then I hate me." The voice was quiet, but with the as much determination as ever.

Nightmare Moon grinned wolfishly in a way not even Sombra with his fangs could match. "That's hardly news, Luna. You hated yourself for the long years you were certain it was all your fault. You'd still hate yourself even if I weren't here!"

"At least I know what love is."

"That's your retort? Really?"

"Yes. Because it drives you nuts that I remember something good after the misery you put me through."

"How many times must I say it, you pathetic filly? I AM you! Your misery, your anger, your jealousy, and your power are all mine! And yes, even, your love and your memories are mine."

The hatred slammed into her again, but she managed to remain upright this time. "Then how come I can hurt-" she cut off with a sudden scream.

"For the same reason I can hurt you. Except I'm stronger than you because I am a grown mare, while you are just a shy little filly, too weak to even take what's yours, much less claim what you want."

There was no response, but she could definitely feel the weight of Luna back there.

"What, cat got your tongue?"

"I'm the filly and you the mare?"

Nightmare Moon snorted. "Of course."

Silence once more.

"This is getting tiresome. You are no more than a ghost of who I was, yet you insist on-"

"Sister's singing."

"STOP INTERRUPTING ME!"

"Then shut up. She finally finished that lullaby."

"What the hell-"

"Shush."

She couldn't believe it, but Nightmare Moon found herself complying. As the silence went on she returned to her pacing. Then the everlasting sobbing resumed.

"Oh for-" Nightmare Moon snapped. "SHUT UP!"

"I will get rid of you, parasite!" Luna hissed in response. "Even if it takes me ten thousand years, I will get rid of you!"

"Stop that 'parasite' nonsense! I am you, idiot! How many times must I repeat myself?"

"You were right. I hate myself, I have for a very long time, and I'm not sure if I'll ever stop, but I'll always hate you more, and that will keep us apart, and my love will make me the better."

Nightmare Moon gritted her teeth. "I am doing this for love!"

"And garnered only hatred."

"You are hated as well."

"Why do you think I cry?"

"Because you are pathetic and sad about losing something you never had the guts to claim, anyway!"

"Parasite."

"And you will never be rid of me!"

"I have an eternity to wait, and I need only a moment. If I can never be rid of you, if I can never truly regain my body, or at least not in time to stop you, then I can end our lives together!"

"And the world with us?"

"It's a sacrifice I'm willing to make to get my revenge."

Nightmare Moon threw back her head and laughed. "You don't need me to be insane, you're already far gone!"

"Good, then you can't hurt me more than you already have."

She would have retorted, she would have sent another wave of pain at Luna, she would have done something, but just then the accursed voice reached her in song:

"Once did a pony who shone like the sun
Look out on her kingdom and sigh
She smiled and said, "Surely, there is no pony
So lovely and so well beloved as I""

She sounded so proud, so unperturbed, so unrepentant, that Nightmare Moon let out a roar of rage that should have raised a tornado of moon dust had there been any air. Blind and unfeeling with fury she struggled once more against the bonds that held her down in vain with visions of ripping the white coat of the pony that dared call herself her sister to shreds and watch it get soaked in blood, feel it tear and taste the hot metal of the scarlet blood and hear the sobs and whimpers and how she would laugh and laugh and how the ponies of Equestria would bow down before her with their precious Princess lying broken on the ground where she would rot away over the years.

Luna returned to her crying, trying to block out the memories of what she had done with the song Tia had sent her and her sobbing. She had let that one verse slip into the mind of Nightmare Moon to get her to be quiet, she couldn't stand the contact between them, between herself and that filthy, hate filled pony that surrounded her on all sides, because in the end she was right.

Nightmare Moon was Luna and Luna was Nightmare Moon, they were one and the same and she had done all those horrible things she so desperately wanted to forget.

She hoped her sister could forgive her.

She hoped she could forgive herself.

Last line ambiguous on purpose. Or coincidence. Doesn't matter.

The piece of song gratefully stolen from ponyphonic's Lullaby for a Princess, which you're probably familiar with, and which should be canon. I want Celestia to have at least one song.

Please review and tell me what you liked/disliked.