"Celestia! Sister! Help... me!" Princess Luna called out, pain clear in her voice. "Please!"
"Luna, what's wrong?" Celestia asked hurriedly, scared from the pain her sister was in, rushing into her sister's room to help her in her time of need.
"It hurts... so bad, sister." Luna coughed and sputtered, her eyes heavy from crying.
"What hurts? Where does it hurt, sister? Let me help you!" Tia yelled, tears sliding down her face, fear clear in her voice as it cracked.
"The darkness... it's... it's so cold. Don't let her take me! Please! Don't let her take me!" Luna was now sobbing, her voice cracking as she cried.
Luna's flowing mane started to calm, and her fur color was lightening.
"Luna, tell me what's going on! If I don't know I can't help you!" Celestia shouted, now angry more than scared.
Luna seemed not to hear her. She seemed like she didn't care either.
"Let me help you!" Celestia barked, grinding her teeth as she only received silence.
"I... Sister, I love you." Luna smiled, more tears escaping her face, her emotions changing and changing.
"Luna... Luna, it'll be okay, I promise!" The Princess of the Sun tried to ease her sister into a state of tranquility.
"No, sister... I'm afraid I've become... a little bit jealous of you..." Luna confessed.
"Luna, no... why would you be jealous of me?! Calm down... don't go..."
"I saw how much our ponies loved your sun... and how much they loathed my moon and night." Luna spat, venom tied to each of her words. "I saw how happy they were... and I hated it. I wanted to be you, sister. I wanted to be loved like you."
"But you are, you are Luna! You are!"
"I-I'm slipping away... into this darkness... She tells me that her name is Nightmare... She lives off my jealousy, sister. She wants to make night eternal. Don't let her... no matter what. Promise me this, sister." Luna held her sister's hoof tightly.
The stars in Luna's mane started to shed and die, and her mane started to get shorter. The transparency faded, leaving a solid lighter blue. Her coat became lighter, leaving her in a weakened state.
"Luna?"
"I'm... not... Luna." The monster hissed from Luna's lips.
"What... Luna..." Celestia peered into the eyes of the mare before her.
Luna's eyes were now a draconic form; becoming a greener color than her lovely blue eyes were, matching the envy in her heart. Her coat was now as black as the night, and her ethereal mane whipped in the absence of air. Her teeth were pointy; almost cartoon like.
"Luna... no, it doesn't have to be like this... Luna! Come back, Luna!" Celestia called, not noticing being levitated in the air.
"Please, your sister Luna is gone forever. Now there is only room for Nightmare Moon."
"No, no sister! I am right here! That's not me, that's not... me. She... she cannot see me." Luna said, looking out of Nightmare Moon's eyes, unable to be heard.
"Give Luna back-"
"The night shall last... forever! Aha ha ha!" The beast cackled.
"No... I made a promise to Luna!" Celestia gathered herself, and bucked Nightmare in the neck. "Tarnishing my dear sister's name and body by behaving like this is... it is... horrible, disgusting, and wrong! Silence, you will not have any power here!"
"This is my body now, Celestia. And this is my kingdom now." Nightmare Moon created clouds and attacked Celestia with lightning, hitting her and knocking her down.
Celestia lay on the floor, crying and upset. Nightmare Moon rushed downwards, pushing her straight through the wall and out into the light of the now setting sun. They took to the skies, golden and midnight blue bolts and rays attacking one another. Celestia went for a hyper beam spell, but was left in the open while it charged. Nightmare shoved her downwards, into where their-no... no, Celestia's and Luna's crowns sat. This thing wasn't Luna anymore. And it was Celestia's job to stop this monster in blue armor.
Celestia levitated her and her sister's crown and fused them, created a crown with a sun on the top. She placed it on her head and cast her spell. The spell seemed to backfire; it closed in on Celestia, but then spread out as Nightmare tried to hit her again, pushing the monster, as well as the younger sibling away, and into the moon that now stood in the sky; Luna knew what had to be done, so she moved the moon with the last of her strength, and lost consciousness.
Luna and Nightmare Moon were banished to the moon for a thousand years. A thousand years. A thousand years for Celestia to think of the ways she could've helped, but didn't. A thousand years for Luna to think of the ways she could've handled this, but she didn't. A thousand years for Nightmare Moon to think about her next attack plan. A thousand years of shame. A thousand years of fear, and a thousand years of regret. A thousand years of planning. All still creeping by, as slow as a slug, as slow as molasses, as slow as time would allow. Slow... slow so they would remember and know how to avoid it. Because they knew it would happen again. Celestia and Luna knew that Nightmare would try this again; she didn't seem like the type to always give up.
Luna would spend the next thousand years during the day listening to her sister's Lullaby, and giving her sister her reply when the Sun Goddess' head hit her pillow.