A soft rumbling noise and the ground shaking were all it took to awaken the deep blue mare that night. Luna got up slowly, amazed that it was night already. She took a look around at the barren, rocky ground that extended off in all directions into a black, starry sky. She hadn't been keeping track of how long she had been here, but she somehow felt that tonight was the last night of her exile. She would be able to escape the moon tomorrow night.
Luna stretched her legs slightly, trying to be as ready and alert as possible. She had been planning for this night for almost 1000 years, and she was determined not to mess up this time. She used her unicorn magic, summoning a few scrolls and quills before her; she had lost the vast majority of her magic when she had been exiled to the moon by her sister, but she had once been a goddess. Spawning these trivialities was nothing for her, even in her weakened state. She magically unrolled the first blank scroll and brought her quill to it, beginning the task that had become part of her daily routine almost 700 years ago. Slowly, she began to write.
The last line blurred slightly as a few tears hit the page. Every night for the past hundreds of years, she created a few scrolls and began to write down her beloved sister's name, over and over, until it filled the page. She would never forgive herself if she forgot Celestia's name, and this was the simplest way to make sure she always remembered it.
A few hours later, when she had finished her task and placed the scroll in the mountain of other scrolls she had finished over the years, she set to work on her next task. Again, she opened up a blank scroll and put her quill to it. But instead of writing, she began to draw. She drew her sister for hours, in a variety of magnificent and regal poses, each one more beautiful than the last. Luna took great care to get the details of her drawings as perfect as possible.
She stopped for a moment before finishing all of her pictures, which she rarely did. Tonight was a special night, as it was the last before the 1000 year anniversary of her becoming Nightmare Moon. But she wasn't Nightmare Moon anymore, and had no desire to be her ever again.
At first, when she had been sentenced to the moon, she did nothing but rage and plot her revenge. It took about ten years for her to understand just how long she was going to be stuck there, and how lonely it was going to be. That was when she removed her Nightmare Moon armor and destroyed it with her magic, never wanting to see it again. She felt guilty for what she had done, and missed Equestria deeply. She missed the kind ponies she had hurt with her cruelty, she missed the beautiful, bright sky and the green grass. More than anything, she missed her big sister. That was when Luna had realized that, even thought it had only been ten years, she was beginning to forget what Celestia looked like
Knowing that had hurt her the most. She was aware that there might come a time when she would not be able to remember what her sister looked like at all. She then had concentrated all of her power, and summoned a scroll and quill to the moon for the first time, and began to draw. Her skills as an artist weren't very good, but she was determined to get better by drawing Celestia every night, so she might never forget what she looked like. A couple hundred years later, she decided to write her name down over and over again, so that it might be burned into her mind and she would never forget the sister she loved.
Finally finished with what might be the last drawing she would ever do on the moon, she carefully placed it on the very top of her personal mountain of scrolls. Every drawing of her sister, every repetition of her name she had even written was on these scrolls that reached high into space. Perhaps this mountain reached as high as the royal castle in Canterlot did.
Glancing away from her efforts, the mare looked towards the bright stars, waiting anxiously for the time they would return her to her sister. It was less than 24 hours now before they would be reunited again. Sadly, Luna wouldn't be able to take any of the drawings or writing she had done while on the moon - the legends said that the stars would return her to Equestria, and her alone. She would have nothing to remind her of her sister.
What was she thinking? Of course she would! She would be united with her sister again, in flesh and blood. She would be able to hold her and apologize, to feel her warmth and hear her voice. All in less than 24 hours.
Luna took a longing look at her beautiful home planet. Equestria had never seemed closer to her, or more beautiful. Nor had Celestia. However...
Every night, though the goddess would pull the moon across the sky, she would never approach it. The connection between the sisters had been faint for almost a thousand years, and Luna noted with a pang that tonight was no different. Celestia had not come any closer to her sister's prison than ever before. Had she still not forgiven her?
"Of course not," Luna said to herself. "Even I still can't forgive myself. I committed an inexcusable crime and turned against my sister, and all of ponykind. I deserve to be here forever." Her ears drooped and she started to cry again.
Hours passed before an idea had come to her, horrifying her. What if Princess Celestia truly hadn't forgiven her at all? What if, as soon as Luna returned to Equestria, the princess would use the Elements of Harmony to seal her in the moon again? Even if it was what she truly deserved, she couldn't stand being away from her sister for another thousand years.
It would be hours until she would escape. She had time to plan, though she didn't like any of the options she had come up with. The only thing she could do was capture her sister before she was exiled again. She would have to use her most powerful magic, and do what she had tried to do that got her sealed in the moon in the first place.
The worst part was, Luna knew she didn't have enough magic in her current form to seal Princess Celestia. Nearly throwing up at what she had to do, she once more summoned the Nightmare Moon armor with her magic. She sobbed and choked as she got into the hateful, jealous armor. It represented everything she had been when she was lost, but it was also very powerful. Without it, she stood no chance against her older sister.
Nightmare Moon looked again at the tower of scrolls she had created, wanting desperately to take them with her. Even if she sealed Princess Celestia within her own heart, she would never be able to see her face again, nor hear her voice or feel her warmth. She would never be able to apologize.
"I know," she said slowly. "I'll keep the moon up forever again. Only this time, I'm not doing it out of jealousy or spite. This time, I'm doing it out of love. Whenever I feel lonely, I'll be able to look up at the moon and remember these scrolls that are here, and I'll remember my wonderful sister. Everypony in Equestria will be reminded of Celestia's wonder every time they look into the night sky. This will be my eternal tribute to her, and no one will ever take it away. I will defend the night at all costs."
The stars began to surround her, pressing their magic against her body. She felt lighter than air, and slowly began to fade away. Nightmare Moon wiped the tears from her eyes. She would have to be strong, so everypony would remember Princess Celestia as strong. The princess would always be remembered as a brave, indestructible pony if only her sister could present herself as such. Nightmare Moon vowed to never cry again.
Even though she knew she would never have another happy day in her life.