There had once been a time where Nightmare Moon was a wandering spirit, twisted and corrupted from what she once was by loneliness and despair. As she descended into madness, she came across someone else facing the same depression, Princess Luna of Equestria. Bound together in their smothering darkness, they set out to force a world to change to what they thought would be their salvation, where they would be loved and adored. In the end they failed and those that they saught to force to love them banished them to the darkness they tried to impose upon the world for 1,000 years. And when that banishment ended, the physical being was given salvation, with the one that had pushed her away long ago now showering her in love and forgiveness for what she'd done. However, that spirit that had been bound to her, the only friend that she'd known for over a thousand years, was ripped from her and obliterated by the very force that had cured her madness.
At least, as far as Luna knew.
Unknown to Luna, that which had saved her from her loneliness, had also given Nightmare Moon a chance at a new life, her own life. It took some time for her new life to begin, and she was held under the care under a being that she could neither see nor touch, but her heart could feel and remember from ages far past. That being now gives forth their love for Nightmare Moon to reawaken her, and set her on the path that the Elements of Harmony opened up for her. And this time, though she might not know it yet, she wont be alone. This is her journey on that new path, where she goes, what happens, is all unknown. But, the darkness that once consumed her, the light of the Moon, and even that of the Sun, are all there to guide her and help her grow. Along with the flame of love now left in her heart.