Prologue
"I will rule in eternal night!" Luna heard Nightmare Moon say in her voice. She could feel the burning-cold triumph rising in the mare, as her deathly, airless aura swirled around her in a purple cloud.
She looked down on her sister with grief and remorse. She had just wanted to be appreciated and loved. She had never meant for it to go this far.
Shut up, pony, Nightmare Moon snapped, and she quailed in fear. She gasped desperately at the sweet, warm night air that the mare's momentary lapse had let in, knowing it could be her last. Nightmare Moon didn't need to breathe, and she was slowly starving the young pony possessed by and imprisoned within her.
"Sister, please," Celestia gasped, pushing against the aura around Luna with her own aura of light.
Nightmare laughed maniacally. "Your sister is dead, fool. No one ever escapes from Nightmare Moon. She will be in my clutches forever!"
"No!" Celestia cried, and in that moment Nightmare slammed downwards into her and knocked her out of the sky.
Celestia fell through a window of stained glass and collapsed, lying prone on the hard stone ground of the old castle cathedral. Her side was rent with jagged, bleeding wounds from Nightmare's twisted, barbed horn.
"Luna," she whimpered. "Please. I will save you."
"No!" Luna burst out with despair, and the mare's lips just barely trembled. "I'm too far gone. Save our kingdom!"
"Shut it!" Nightmare hissed, out loud, and in that infinitesimal moment Luna screamed out with all her strength, "Sis, save our people."
Celestia looked up and Luna saw her own despair mirrored in her sister's eyes. Then the dim glow of a new resolve entered her eyes.
A glow emanated from Celestia's horn, and from the darkness behind her emerged six glowing gemstones in different colors. They swirled around her as she staggered to her feet.
"The elements of harmony?" Nightmare scoffed. "Those are just an old mare's tale." But hope rose within Luna as she felt the thin thread of panic working through Nightmare.
Celestia looked up with the rage of regret in her eyes. "So - were - you!" she shouted, and a blinding rainbow exploded towards the both of them.
"No!" Nightmare Moon cried with pure, freezing rage. Unable to release it, the feeling swirled within her and attacked the only thing it could find: Luna.
Luna felt herself detach, floating, even as they sped upwards towards the distant moon. Cradled in benevolent darkness, she fell away into the void as they slowed and landed on the dark side of a world of infinite cold.