Luna.

“What is it that you want,” Luna said flatly, her voice echoing in the empty Lunar Limbo.

The thing that called itself “Nightmare” floated in front of where Luna sat, its gaunt, pitch skin transparent so one could view the magic that flowed through it: cold, concentrated at the heart. A smile stretched unnaturally across its face. A fanged cheshire grin. Can’t a friend say hello?

“You are no friend of mine, Nightmare.”

Come, Luna. We have been together for so long, planning for so long, we might as well be friends.

“Spending time together does not a friend make. A friend would have told me that was an awful idea. A friend would have convinced me not to gain control of the nation. A friend would have tried to calm my rage. You are no friend. You are the devil,” Luna spat.

Nightmare’s grin somehow grew larger. The devil? Wouldn’t that be calling yourself a devil as well?

“That is not the same! You are the one who coerced me into those crazy schemes!”

It is not coercing if you were willing to do them.

“Willing to kill my sister? Are you crazy?! I would never dare—”

And yet you nearly did.

Luna took a few moments before replying, “‘Nearly’ is not ‘actually.’”

Nightmare chuckled. Luna Luna Luna. Stop denying the truth.

“I am not denying anything,” she said stubbornly.

Sure you're not. You can't fool me, Luna.

Young Luna kicked a lunar rock, and it tumbled away before being flung into the void above.

The moon was dark, cold. Unforgiving. Lunar Limbo, in contrast, while dark, was kinder than the moon. The magic that held her here was warm and loving, as if it wanted to protect her. Were it not for that, Luna may had already plummeted further into despair than she was.

Not that Nightmare was helping.

Its ghostly mane and tail rippled as it flapped its inky wings, the feathers limp and rotting. Eternal night would have been wonderful, Luna. If only you had not held back.

Luna looked around before saying, “I don’t want eternal night. Not if it feels like this.”

Powerful? Vigorous?

“Cold. Impersonal. Lonely.”

Nightmare sneered. Mortal emotions. You are above that, Queen Luna.

“Do not start that again! I am not a queen!”

And now you no longer will be able to be one.

“Why would I want to be a ruler of the dead?” Luna said quietly.

Who said they would be dead?

Luna gestured around her, to the void above. “No sun? No light? Ponies cannot survive without it. They would become malnourished, husks of themselves.”

We would develop crops to survive—

“‘We’?” Luna snorted. “I never thought that far ahead! I am merely a teenager in alicorn terms, you demon! All this was on impulse. You, of all beings, should know that.” She turned away. “I should have never helped you that day, in the rain.”

Nightmare attempted to place its rotting wing on Luna’s back in self-serving comfort. You did the right thing. I helped you.

“You did no such thing,” Luna said, pushing the appendage off with her own wings, shivering when they touched Nightmare’s wing. “You made everything worse. The only good thing you did was keep me company when I was lonely. I no longer need you. I would rather be lonely than be with a destructive being like you.”

Like your sister no longer needed you? Like no pony no longer needed you?

“Celestia was busy. Ponies need their rest. Not everypony can stay awake during the night like you and me.”

There you go, making excuses for them. Nightmare crossed its skeletal forelimbs, frowning. They abandoned you, Luna. Ignored you. Ostracized you. It bared its dagger-like fangs. When will you stop being so soft?

“This ‘softness’ is what kept me alive,” Luna said firmly. “It’s what prevented me from becoming totally like you, from completely bonding with you. You are a parasite, you are! You poisoned me further for your own benefit!”

A parasite? Moi? Nightmare put its shadowy hoof to its chest in mock hurt. Not I. I am a simple symbiote. Nothing more.

“You are such a liar,” Luna hissed through her teeth. “You said you would help me. You did, yes, but at the cost of my sanity. You said you would revive my friends. What would that have cost? My soul? You are nothing but a liar and a thief.”

The being chuckled, a sound not unlike a skeleton being crushed. I never lied. I just didn’t tell you some things. It’s not the same.

“It is exactly the same. Omitting information is the same as lying.”

Don’t be a hypocrite, Luna.

She sighed in defeat.

Silence reigned for what seemed like years. Luna kept her back to Nightmare, who flapped its wings every once in a while.

Finally, Nightmare spoke up. Want to play a game?

"No. Your games are often more trouble than they're worth, and dangerous too."

But this one isn't.

"Yeah, right."

It isn't. I promise.

"Fine. What's the game?"

Nightmare grinned maliciously. It's called "Y'know." Simple: You say something, starting with “y’know.” You start.

“Okay… Y’know, this game doesn’t sound as bad as I thought it would be.”

Y’know, this place isn’t so bad.

Glaring at Nightmare, Luna said, “Y’know, you have little to no regards for others’ feelings and thoughts.”

Y’know, I do have regards for feelings, such as yours.

“Y’know, you only paid attention to my negative feelings.”

Y’know, this place is actually a great place to be.

Luna bristled. “Y’know, I don’t know the reason why you would even think that!”

Y’know, I thought you would have thought what I thought.

“Y’know, I have no clue why you thought that!”

Luna. This is a great place to be because we can be away from distractions and ponies so we can plan. We need to be prepared!

“Away? Away?! I would have rather stayed! I wish the Elements had stripped you away instead of banishing the both of us! I wish they had killed you!”

Aw, but we work so great together. I mean, the assassination almost went off without a hitch…

“Okay, that’s it!” Luna gathered her energy and formed a sapphire blade with her magic. “That’s enough!” she said, pointing the sword. “No more!”

Nightmare’s grin grew larger than ever before, as if she had wanted this to happen. She, too, created a blade, hers of obsidian. Oh, this will be fun.

As soon as she did, Luna charged, swinging her sword haphazardly. Nightmare easily sidestepped. Luna skid to a stop, Nightmare teleporting in front of her. It calmly but swiftly hit Luna with the butt of its sword in between her eyes. She stumbled back, dazed.

Without waiting, Nightmare smacked Luna with the flat of its blade. She yelped and then growled, swinging hers at Nightmare's ghostly leg. The blade slipped through with no evidence of its intrusion.

Nightmare's cheshire smile grew, its eyes becoming wide and crazed. It flung a multitude of pebbles its host. Luna swore and tried to deflect them with her sword. Nightmare simply chuckled at her feeble attempts.

You can't defeat me! it roared. Not if you need me!

"But I don't need you! Not in the slightest!"

Nightmare conjured up a giant dragon. Luna snarled and obliterated it with one blast and a few sword strikes. Finally, Luna managed to try and attack Nightmare, who blocked the swing.

Their swords clanged against each other in a blur, the colors combining to create an indigo arc. Luna could not parry many of the monster's attacks, throwing up a shield before she could get hurt. Nightmare could parry all without breaking a sweat.

Nightmare twisted Luna's sword out of her magical grip and placed its obsidian blade on her neck. Do you yield?

Luna panted, glaring. "What do you think, you monster?!"

There was a sudden burst of light, followed by a measure of heavenly music, and a rainbow tunnel appeared behind the monster. It turned, screeching at the light, and Luna took the opportunity to knock it off of her.

Home! Luna thought, beaming.

The tunnel was calling to her. It filled her with the warmth that being with family creates, and called to mind so many happy memories. She heard her sister speaking, presumably to a scribe or a scribe spell, based on her tone.

"... there is more to a young pony's life than studying, so I'm sending you to supervise the preparations for the Summer Sun Celebration in this year's location: Ponyville."

"Tia?" Luna whispered. She walked slowly towards the tunnel, wings spread in preparation for flight. " I'm coming home, Tia. Alone."

No! Nightmare hissed. You are taking me with! It tackled Luna, and they tumbled into the rainbow tunnel.

"Get off!' Luna screamed, swinging her limbs at Nightmare. "This is my chance to get home!"

It is a chance for revenge!

Luna cried out as Nightmare combined with her, muting her consciousness. She managed to speak one thing: "Tia! Run!"

Nightmare, now in control, spoke through Luna's mouth. "Ponyville, eh? Let's go pay your dear sister a visit."

Luna could only cry.