"Celestia?" Princess Luna glanced at a relaxed white Alicorn mare sitting by a lake, her multi-colored mane dipped in the water. "Sister, what's been keeping you so distant lately? It is almost time to lower the sun. You know your task is to bring forth the moon." Celestia looked at the kingdom beneath them, and their subjects played in the day her elder sister, Luna, brought forth. Luna looked through the clouds and focused on her subjects. "What on earth are you looking at? Come on, dear sister. Those playful ponies will be wondering where their precious moon is." Luna tugged on Celestia's tail.
"Yes..." Celestia mumbled. "Just give me a minute. I need to... think." Luna frowned.
"Yes. But time's running out. You know how much of a magical preparation goes into even attempting to do this sort of thing. Make it quick--"
"I can't do this quickly when I can't even hear myself think!" Celestia snapped. Luna jumped back in surprise, before quickly turning away. "Can't you mind your own business?"
"Alright, Princess," Luna said, rolling her eyes. "I don't know why you've been acting like this lately, but that is not the kind of behavior I'd expect to see from a sister of mine, and you know it!" Luna flew off into the castle. "Maybe she's stressed today. But that does not need to come at the expense of our subjects..." Luna's purple aura lowered the sun slowly as the sky turned to a colorful hue. And the moon rose...
"I'm taking care of that!" Celestia said as she flew into the Canterlot throne room. "Have a nice rest, sister. As always, I will guard the night..." Celestia closed the curtains with her magic and flew onto the balcony. "And Equestrian citizens..." Her eyes flashed a bright shade of green. "I hope you enjoy your day tomorrow, for it may be..." Celestia flew up into the sky and landed on a plush silver cloud overlooking Canterlot. "...your last."
The next evening...
"Celestia? It's time to--" Luna walked through the castle hallway into the throne room to see Celestia staring at her angrily.
"Not another step!" Celestia's voice roared. Luna stopped dead in her tracks, seeing the flame in Celestia's eyes. "Did you really expect me to stand idly by while they all basked in your precious light?!" Luna slowly shook her head, careful not to antagonize her sister, looking as though she were a cat ready to pounce. "There can only be one princess in Equestria... and that princess will be me!" A simple stomp of her hooves cracked the walls beside and above her. Suddenly, the force of the blow broke the stained glass window above them.
"Celestia! What are you doing?!" Luna shouted. But it was too late. Celestia's magic reflected the bitterness in her heart, and rose the moon... and kept it in place in front of the sun. Luna tried to make either the sun or the moon go down, but her magic was useless compared to how powerful Celestia's magic showed to be.
Celestia floated back down as the power of the eclipse surrounded her, and seeped through the Alicorn mare's coat. A multi-colored blinding light grew brighter and brighter until even Luna, Princess of the Sun, couldn't bear to watch anymore. But eventually the spinning orb grew darker. Luna watched in horror as a terrifying silhouette of Celestia transformed into what seemed to be a... vampire? Bat pony? Celestia stepped out of the dark smoke that surrounded her. Her coat seemed to be black now, and her hair was only light pink. She also seemed to be... bigger in size.
Celestia's evil laughter echoed through the castle. Her magic shot up into the air and destroyed the half the roof of the throne room... quite easily. Luna knew this new creature may be a threat to their kingdom, and Luna would do whatever it took to restore things to normal...
Luna flew up into the air, but Celestia shot at her with her dark magic. Celestia missed, and blew another hole into the roof that remained. Luna returned to the ground.
"Celestia!" Luna faced the anger in Celestia's eyes. "I will not fight you! You must lower the moon! It is your duty!"
Celestia stared at Luna in a look that said, You can't possibly be serious.
"Celestia?! I am... Nightmare Moon." Luna stepped back. "I have but one royal duty now... to destroy you!" Celestia blasted at her sister, but Luna quickly flew up into the air and out of the castle roof. Celestia chuckled.
Wherever Luna flew, Celestia followed, trying to hit Luna with her dark blasts of magic. She always missed, and hit other parts of the castle. Celestia chuckled. "You want to play this the hard way? We'll play this the hard way!" Celestia blew one more blast of magic at Luna, which, to her luck, hit Luna right in the neck.
"Aaaaaighh!" Luna screamed as she lost consciousness and fell to the ground. Celestia laughed maniacally as she floated in front of the moon.
Luna's body lay motionless on the castle floor...
Minutes passed before Luna got up on her hooves again. She sighed, her voice turning to whisper. "Celestia, dear sister. I'm sorry, but you've given me no choice..." She grabbed the Elements of Harmony with her magical grasp and flew up into the air with them. They revolved and spun around her body, engulfing her in a colorful flashing light. Celestia looked right at the colorful jewels spinning around her sister, recognizing exactly what they were. Celestia tried to fight, but the rainbow power of the Elements were just too strong. They resisted Celestia's dark magic, and shot her permanently to the moon...
Luna took on responsibility for both sun and moon, and Equestria has been safe from Celestia for thousands of moons since.
"Princess Luna, it's almost time to raise the sun for the celebration! You don't want to disappoint those ponies by not giving them the longest day of the year, hmm?"
"Just a minute, Inkwell," Luna said, looking at all the banners.
They were all just reminders that she needed to banish her own sister permanently.
