Luna, as per normal, had just started to perform her daily task, that of lowering the moon. Lately, the Princess of the Night had been quite content with herself, her existence, her meaning, her subjects. She had always known that the ponies of Equestria had slept through her nights, bar the few who had stayed up studying or working or reading. There had always been the handful of ponies that spent their nights awake, but they had locked themselves up, shunning the light of the moon and instead basking in the glow of candlelight.
The Princess was lowering the moon, wondering why it was that everypony shunned the most beautiful time of the day, to wait for her own sister's sun-filled day. Why was it, that nopony ever basked in the light of her moon? Why was it that her sister was more beloved by the land, despite Luna bringing the cycle that would dictate tides, mark significant events and keep track of the year? The Princess had pondered over these thoughts for the last few days, but it was only now that she saw what needed to be done. She knew the night would have to last. Permanently. It was now that Luna saw the truth, and saw what this meant. If her co-ruler and sister was preventing her from being loved, she must solely reign over the land. She must endure, while Celestia must fall.
The time had passed, and the thoughts had passed over her head one more time. The sun would never rise again. The Princess sat in the throne room, her sister unusually absent. The sun would set for the final time tonight, and Luna would rule the land solely, with the land gripped in an eternal lullaby.
Celestia entered the throne room, her mane flowing gracefully as ever behind her. "Not another step. Did you really expect me to sit idly by while they all basked in your precious light?" Luna proceeded to carry on her speech, walking up to the balcony. "There can only be one princess in Equestria, and that princess will be ME!" She unleashed her rage upon the balcony, striking with such great force it had shattered the wall above her. The sun shone brightly into the throne room, but not for long. Luna used her power to raise the moon, disrupting the balance of day and night, gripping the world in a blanket of darkness. The sheer hate and darkness had begun to transform her into a being of pure hate and evil. Dark energies seethed around her body, enveloping it in a glowing red sphere of energy, physically transforming her, draining all light from her.
Letting out a laugh, all traces of the sun had disappeared and the night had truly covered the land. Unleashing her new powers, she let out a beam of magic, destroying everything it touched, slicing a hole in the roof and shattering several statues. Celestia stood forward and took to the skies, with the newly transformed Luna unleashing her might. The solar princess avoided the blast of magic, and landed gracefully.
"Luna," she proclaimed, lowering her wings. "I will not fight you. You MUST lower the moon! It is your DUTY!" Her voice had a tone similar to that of fright, but also that of sadness and command.
"Luna? I am... NIGHTMARE MOON!" The once Princess of the Night dubbed herself anew. "I have but one royal duty now: TO DESTROY YOU!" The Ruler of Night, once a princess, unleashed her wrath upon her sister, just missing. Celestia lifted her wings and took to the skies once more, rising out of the now ruined building. "And where do you think you're going?" Nightmare Moon commanded.
In the skies, Nightmare Moon started unleashing her full power, striking buildings left and right, but each time missing her sister. Celestia pulled left and the once Luna let her might soar through the sky, striking her sister down. Celestia let out a yell of pain and plummeted to the ground, down, down, down. Satisfied at last with the apparent defeat of Celestia, Nightmare Moon reveled in a hysterical laugh.
Celestia lay unconscious in the ruins of the once great city on her side. She let a groan of pain out and rose to her hooves, defiant of the once princess of night's new reign of terror and power. "Oh dear sister, I'm sorry, but you've given me no choice but to use these." Her yellow aura raised a hidden platform into view, setting of a series of mechanical reaction, raising a planetarium-like structure, with five brilliant gems in place of planets: the Elements of Harmony. Celestia grabbed each of them within her yellow aura, revealing a sixth, but this one a star. The Solar Princess activated the Elements, a light now radiating from her magical shield.
With a visible tear in her eye, Celestia raised herself into the sky, hovering across from Nightmare Moon, who herself focused her powers, prepared to take her sister down once and for all. Celestia, the older sister of Luna, prepared herself as a bolt of searing magic was thrown at her. She unleashed the powers of the Elements of Harmony with a heavy heart, knowing entirely what they would do. As the bolts of energy collided, Celestia released but a single tear from her eye, and quickly she overpowered her sister and a bright ball of fire engulfed her. She let out a desperate cry, but nothing came of it. She was sent away, to the moon.
A brilliant blast of all the colors of the spectrum surrounded the moon as a shadow appeared on it. A figure of a mare appeared on the moon, to serve as a reminder of the prison for this terrible act.
Celestia lowered herself to the ground, sobbing gently. "What have I done..."