Blackness. That was what greeted Luna's eyes when she first awoke, and she almost didn't believe what she saw. It was... empty. A stark, blank void with seemingly nothing but herself, drifting in a sea of loneliness. Sitting up, she glanced around fearfully, feeling herself slowly turn back into the Luna she was. "Hello...? Tia...? Anypony?" she asked, her voice slowly dropping in pitch as she lost what shreds of hope she had managed to hold on to.
Realisation washed over her, and the Moon Princess' eyes widened and her lower lip trembled. Curling in upon herself, she began to cry. The emptiness was suddenly filled with nothing but her voice, and she felt herself shake as her morale weakened. She had been banished. A punishment reserved for the most serious of criminals, Luna never imagined herself to one day be on the small globe that was the source of her powers.
Eventually, her cries began to die, and she sat up again with a small hiccup. Rubbing her eyes, she sniffled a little before standing up fearfully. She had never felt so alone.
Taking a good look around herself for the first time, Luna gasped when she saw the small speck far, far below her which was what she assumed to be Equestria. It was so tiny, so insignificant, just a speck in the endless void... Exactly how she felt. Exactly what her night was.
Looking still further, she saw a glowing, golden, molten mass that shone like... the Sun, her sister. It's brilliance almost blinded her when her eyes rested upon it, and she felt herself grow angry at it due to all the memories it brought back.
Her rage began to grow inside her, until eventually she could take it no more. Letting out an angered scream, she grinned when she felt it shatter the silence. Her coat once more began to turn inky black, as if liquid had been spilled on her and her armor reappeared on her body.
Here. Even here, in the emptiness which was her home, she could never get away. Even here, in the vast space which could be filled with so much more was nothing but the Sun in the middle, the day the most important. Here, she was still nothing, and her night could never shine.
Nightmare Moon laughed. A long, cold laugh, it was nothing but mockery and pure evil, not a speck of the Luna that once was.
"Hah. Typical of you, to rub your victory in my face even now." she growled, studying the sun with her now improved eyesight. She didn't see anything good about it. Casting her eyes back to Equestria, the former-princess smiled.
"Mark my words Celestia. For when I return to your pitiful world, I will bring with me the cloak of an eternal lullaby. The day I return... that day will be your last."