Shaking with rage, filled with a powerful magic she did not possess before, Luna fought against the combined power of all of the Elements of Harmony with as much of the strength that she could muster. The power surged out of her horn in turquoise light, aimed at her sister, Celestia. The golden light of the Elements glowed, protecting her from harm.
How dare she! How dare she fight me! How dare she use our elements against me! Thoughts flicked through Luna's head, urging her on, filling her with more and more fury.
But then the golden light grew brighter, coming closer, almost blinding her. She was losing! How could that be? Luna had the most powerful magic anypony in Equestria had ever possessed! The elements were nothing compared to that. The blinding light was gathering speed, extinguishing her beam, coming closer... Closer... Closer...
But an extremely strange thing happened. As the beam that would surely kill her came closer, it just... Left her. Everything. All her rage, jealousy, anger, fury left her. Celestia was about to kill her! Her own sister, her beloved sister was about to end her life and she was crying, looking away, covering her eyes as her own magic came soaring towards Luna...
No! Wait sister! Please! She tried to cry out, but all she could scream was "Noooooooooooooo!" as the light engulfed her and in a blinding flash, everything went black.
Waking up hours later, Luna groggily raised her head, wondering where she was and why her head hurt so much. Confusion clouded her mind... where was she? It was very dark and Luna couldn't make out a thing, but everything felt strangely familiar.
Every bit of her ached, but her head felt as though she had suffered quite a serious blow. Gingerly lifting her hoof, she discovered a large bruise marking her fur.
Putting her hoof to her head, she felt her mane. It was soft and still, it wasn't flowing and surging with power as it should have been. Her head was aching and Luna was feeling very dizzy as if she had been spinning for hours. She tried to cast a simple light spell, but even that hurt so much that she cried out and grabbed her horn with her hoof.
What was this place? Why was she here? And where was her dear, sweet sister, telling her it was going to be ok?
And then it hit her. She remembered everything.
Luna had attacked her own sister in a jealous rage, tried to harm her... kill her.... And she had.... She had almost succeeded.
It was almost too much to bear.
Burying her head in her hooves, she tried very hard not to weep. She didn't care where she was, or why she was in so much pain. She cared only for her sister and the anguish she would be in now.
Luna knew this place. It was the moon, and she was locked inside it, as a punishment for her deeds. And she deserved every bit of it.
And then the moon was tingling with power, unfamiliar power that did not agree with the moon, the complete opposite. Bright gold light filled the interior.
It was solar magic, Celestia's magic, and it was not meant to make contact with the moon.
There was no one else left to raise the moon, Luna realised, now that she was gone. But Celestia couldn't do it. Only she could do it.
So Luna helped her. The pain was excruciating, but Luna pushed on, tears welling in her eyes. Her sister could never raise the moon, but Luna could and would help her to.
After what seemed like hours, it was done. The moon was raised. Her painful work was done. And Luna succumbed to her tears.
Thousands of years went by. Luna did not know. Luna did not care. The only thing that she cared about was her sister and how she had harmed her.
I'm so sorry Celestia... I only hope that one day you might forgive me.
Where she was, the only thing she could do to ever deserve forgiveness was help her sister every night.
But why? Why is it like this? What happened to me? And why am I here?
Luna didn't know. It occurred to her that she never even felt jealous, upset maybe, but never jealous, of her sister before that blinding fit of rage came out of nowhere. But it was her own fault she was here, no one else's, and Luna was going to apologise. She would never blame anyone else for her own actions ever again.
She would make sure of it.
It was all planned out. Luna knew how to escape, it was very simple. The stars were going to help her to escape, open a way out. And then Luna would apologise and take her punishment with good grace (she deserved every bit of it), and everything would go back to normal. The sisters might even be sisters again, even if Luna lost her Princess title, which she surely would! It didn't matter to her anymore though.
The stars were coming closer, Luna's magic surging through. Everything was going well. The escape was opening, the light flowing in.
Suddenly, Celestia's solar magic came rushing over her. Golden light filled the moon again. Luna didn't say anything. She was used to it.
And then, everything went wrong.
Her mind went foggy and she saw red. Fury filled her, causing her blood to boil. Celestia had wronged her. Locked her away for a thousand years. It was all her fault.
Luna wanted to hurt Celestia, harm her in any way she could. Equestria would be hers. Equestria would belong to her. Their Princess would fall and she would take her place as Queen.
Her fur turned black, her mane surging with power again. Her teeth sharpened, her eyes narrowed into cat like slits. Luna flapped her new bat wings and smiled. She was powerful again and it felt good. She was Nightmare Moon.
And then... Everything was gone. Her mind was blank. She no longer had a plan. She no longer had any thoughts. Luna knew nothing.