The Moon Princess ducked behind a broken column, her eyes wild, her chest heaving. Such ferocity, such power! She was unprepared, and unpracticed. Where had her sister come from? Where had she been hiding? As if to answer, the top half of the column vanished in a gout of flame. No time to think. Not now.
She gathered her wits and teleported to another vantage point, appearing on a rocky outcrop that was familiar to her. She she had spent many nights here, when she was younger, perfecting her work. She could see her sister, now: bloodied but unbowed. Five smaller ponies stood around her in a ring, each gazing into the night, ready for whatever came.
Of course her sister would have loyalists. Of course she would surround herself with mewling sycophants, even now. The fear in her belly churned into a dark fury. Her fatigue and doubt were washed away in a flood of raw hate. She leapt into the night sky, screaming with frustration.
“CELESTIA,” she roared, her great wings unfurling as she fell from the precipice. “We end this NOW!” She dove for the Sun Princess, for her sister, everything she hated, and everything she loved. Power coursed through her. A lance of night poured from her horn, equaled only by the tears streaming down her face. She knew what she was about to do, but she could not watch.
She never reached her sister. Opening her eyes, she stared in wonder. Celestia stood, regal and proud, as radiant as her beloved sun. Around her, the five ponies floated, suspended in the frozen night air. They were casting a spell - that much she could see - but the type of magic was alien to her. Unicorns, pegasi, and an earth pony - earth pony! - each glowed with a distinct hue, lending their light to her sister, who combined them into a pure white sphere: a sphere which now held her aloft.
Wait! Those colors! The Elements! Her sister had somehow found the Elements!
Suspended as she was, she could see now the regret in her sister’s eyes, the tears that welled at their corners. Her sister... pitied her? Pounding against her prison’s walls, she spat at Celestia, and thrashed, unleashing wave after wave of power against the silvery barrier. An hour she raged, then two, all the while Celestia watched her with sad eyes. Finally, she collapsed, unable to fight any longer, panting.
She could hear a voice through the bubble. “...ry, my friends. I love you, dearly, but I must.” Celestia turned to face her sister. “And I’m so very sorry, my dear Luna.”
The white mare’s brilliance redoubled. A single lance of light shot from her outstretched horn, through the sphere, and into the sky, connecting the earth, the sisters, and the moon. Whatever arcane power she had left she poured into that spell, holding on, no matter how her horn charred, nor how her legs buckled.
As soon as it had begun, it was over. The light flickered, and faded, and the Night Mare found herself gazing upon Equestria from an unimaginable distance. It was quiet here, wherever she was, and so cold. So very, very cold.