Princess Luna stood on her balcony, looking out at her beloved kingdom. A soft blanket of moonlight spread gently across the land as far as she could see. Dried tears stained her face, leaving salty streaks of matted fur on her cheeks and muzzle. No more came, however, as the time for lamenting was over. It was time to act.
The powerful alicorn's horn glowed with a dark blue aura. It wasn't long before the moon was surrounded by a similar glow. She spoke, her voice thick with emotion as she wrenched the words from the depths of her broken soul. "Dear sister... Beloved subjects... Forgive me for what I am about to do."
With a heart as heavy as the object she was commanding, she gave a powerful mental tug, pulling the moon directly toward herself. Though the naked eye could not see a difference, the moon was now on a new trajectory. Instead of moving across the sky, it was on a direct collision course for Canterlot, with more than enough mass and force to completely destroy all of Equestria when it hit. She sighed, shaking from adrenaline over what she had just done.
As the adrenaline rush faded, it was replaced by a slowly building despair. She sank to the balcony floor and wept. Memories raced by in her mind as she recalled all of the noteworthy moments of her life, from her biggest successes to her most humbling failures. Moments of pride and regret. Truths she learned and lies she mistakenly believed. In a moment of clarity, they all seemed to coalesce, the many specific defining moments forming one mass of thoughts and feelings that seemed to simply be... her. This was the final moment it had all inevitably been leading up to, and she saw her current self, the product of her past, no longer with a future to affect. No more lessons to learn, no more changes to make. And she felt regret. She wished she could have become a better mare. For her beloved ponies and for her sister. She wished she could have been the leader they deserved.
She was snapped out of her introspection by a loud knock at her door, followed by the sound of several ponies barging into her room. Celestia, accompanied by two guards, found and approached Luna on the balcony. Celestia spoke first. "Sister, what have you done? Return the moon to its rightful orbit at once!" she said firmly, her countenance grim.
Luna, lost in her despair, looked up at her sister wordlessly. Princess Celestia's expression softened slightly when she saw the depths of the pain her sister was in. "Guards," she said, not taking her eyes off of her sister, "wait outside the door. Don't let anypony enter." After a quick unseen salute, they were out of the room.
Luna looked up at her older sister and tried to speak, only managing to choke out a single word. "Sister..."
Princess Celestia remained serious however, as no amount of emotion was going to stop her from saving her kingdom from certain doom. "Luna," she said, a hint of danger in her voice, "there had better be a very good explanation for this. And fast, because I am about to fix the moon's orbit myself if I have to."
The lunar goddess held up a hoof and took a moment to calm herself and find her voice. Celestia waited patiently, keeping mental track of how much time she had before she would have to intervene herself. Princess Luna didn't need long, however. After several shuddering breaths, she spoke.
"Forgive me, dear sister. We did what We had to for the good of the kingdom. For, you see, as We were making our bed, a spider crawled into it. We searched thoroughly, but could not find it. Now We simply cannot afford to take any chances."
Princess Celestia was taken aback. "A spider. In your bed." Luna nodded solemnly in confirmation. Princess Celestia was stunned. She couldn't believe this was actually happening, and even took a moment to magically pinch herself to be certain she wasn't dreaming. Once she was certain it was all real, she stepped closer to her grieving sister and knelt on one foreleg's knee, wrapping the other around her in a comforting hug.
"Oh, Luna... I had no idea. I'm so sorry." Celestia felt Luna's contagious despair clutching at her own heart, but forced it down. She had many years' experience to help her not succumb to overwhelming emotions, and decided to be a rock for the younger princess. Comforting Luna in their final moments was the least Celestia could do. "I love you, dear sister. I always have."
Princess Luna only wept harder in reply. Princess Celestia softly whispered sweet reassurances into her sister's ear. "It's not your fault. I love you. You are the best sister a pony could ask for. Anypony else would have done the same thing. There was no other choice."
As time passed, the moon became visibly larger in the dark sky. Surely, some ponies were beginning to be concerned. Celestia internally struggled with a decision. Should she go out and try to keep her little ponies calm, or stay with her sister? Either way, once the moon hit, it would all be over. Perhaps it was time to give up being a leader and take some time for herself and her sister. She wanted to spend her last moments here, with her only family. Not out among scared and angry ponies. She snuggled up closer to the lunar princess. The sister she had so greatly wronged... Tears came unbidden as Celestia wept silently into Luna's neck.
Princess Luna didn't even notice. Her eyes were fixed forward, staring but unseeing. The weight of her choice was too much to bear. Dissociating was something she had done a lot on the moon. Everything around her ceased to matter, and she buried herself deep within her mind, away from the world.
In her mind's eye, Luna saw herself in a small, dark room. The only thing in it was a stone pedestal with a dark purple chest sitting on it, lit from above by an unseen light source. The top of the chest was decorated with her cutie mark. The latch on the front was an intricately crafted crescent moon. She approached it with trepidation, knowing what was inside. Using a hoof, she pushed the latch to the side, rotating the moon on its hinge. With a click, the lock opened and the lid of the chest sprung up and back, revealing the item inside. Sitting on a velvety red inner lining was a helmet. It was a single piece of steel. A fierce and sleek form-fitting design, with sharp forward-sweeping edges. Nightmare Moon's helmet. This object used to fill her mind with pleasant fantasies of revenge and power. It used to give her something to look forward to during her thousand years of banishment. Now it was only a reminder of her failures as a princess and a sister. With a sigh, she shut the lid. The chest and pedestal disappeared. She blinked, and was back on her balcony with her sister. She could feel wetness on her neck, and was quick to notice Celestia was crying into it.
"Sister," Luna said softly. "We have been a great disappointment to thee. Nightmare Moon was a grave mistake, and We are sorry for all the pain it has caused. We are to blame for all of th-"
"No!" Celestia interrupted. "Luna, stop right there. You are not the only one to blame. We both made mistakes. I should have been there to support you. Instead, I was only there to punish you when it was too late. I used to think it was all my fault."
"But surely thou did not truly believe thyself to be the sole cause of our transformation to Nightmare Moon," Luna said, incredulous.
"For a long time, yes. I did. Hundreds of years, in fact."
"But how? It was We who caused all the trouble."
"The same way you are blaming yourself now, dear sister. We are our own harshest critics. What happened was a culmination of mistakes we both made. But I eventually realized that the past is done, and the best way to use it is to learn from it and improve ourselves for the future. Not to let it ruin us."
Princess Luna looked up at the large moon sadly. It appeared nearly six times its normal size. "Not much of a future left for us though, is there?"
"No, but I will stay here with you until the end."
The two shared a hug and affectionate nuzzle. They remained in contemplative silence, as nothing more needed to be said for the moment.
Luna, despite the overwhelming storm of emotions she just weathered, suddenly felt immensely calm. It was as if her body sensed the end was inevitable and was making her final moments more bearable. She thought of her mistakes and of how her sister forgave her for them. She remembered how happy she was when Nightmare Moon was vanquished, and she could finally really meet Celestia again. As a sister, not an enemy. And she smiled.
The moon was close now. It filled the sky. Ponies were surely panicking. Celestia thought of the poor guards outside Luna's chambers. They were loyal to the end, likely keeping hordes of panicked ponies from barging inside. It probably helped that they couldn't see the moon themselves.
As the final moments approached, terror gripped Luna's heart, but she kept herself from panicking. "Celestia. Sister. We love thee."
"I love you too, Luna."
The two princesses held each other and watched the falling moon together. As it reached the atmosphere, much of it burned bright orange. Equestria was lit up with blinding light as the entire sky was filled with burning lunar surface. This was it. The end of ponykind.
Then, noticeable even against the fiery sky, the two alicorns saw an enormous rainbowlike beam shoot out of Ponyville, far to the southwest. It slammed into the moon and enveloped it in a multichromatic aura. The fire in the sky stopped as the large object was halted. Then it began to recede. Bits of debris rained down around them.
"No!" Celestia shouted.
"The spider! The moon must fall! 'Tis the only way!" Luna yelled. Her horn glowed as she reached out to the object she was so familiar with, but something stopped her. She couldn't overpower its hold on the moon. Whatever it was, it was even more powerful than her. Then, as she concentrated to intensify her magic, a much smaller rainbow beam shot from the moon and slammed into Luna's horn, knocking her back.
"Luna!" Celestia cried. Her sister was on the floor unconscious. With grim determination, Celestia used her own magic to try to control the moon. She had done it hundreds of thousands of times while her sister was gone. But the same force stopped her as well. She couldn't let the spider get away. She struggled, her horn glowing brightly, as she commanded the moon to fall. Another rainbow beam came from the moon, directly toward her. Celestia knew what was coming and braced herself. As it hit her, she felt herself flying backward into Luna's room and rolling over the marble floor. Then blackness.
"Poison?" Celestia asked. She and Luna were seated in their throne room, only recently having regained consciousness. Twilight Sparkle and her friends were standing in a semicircle before them.
"Yeah," Twilight said. "It makes you lose all sense of proportion when it comes to fearful reactions."
"The spider in our bed..." Luna said. "We can't believe We almost... Because of a spider..." She trailed off, unable to bear the thought.
"It's not your fault, dear sister," Celestia said. "It was whoever poisoned us. How did it even happen?"
"We looked into it. Looks like it was added to your dessert last night. Specifically the cake," said Twilight.
"Not the cake!" Celestia said, as if personally offended. "Who would dare?! And who would want to destroy all of Equestria, themself included?"
"Well, that's the thing. Whoever did it didn't want to destroy everything. They probably just wanted to cause some chaos, maybe make ponies hate you."
"Oh? How can you be sure?"
"Well, once it looked like the moon was falling from the sky, I had a knock on my door. When I opened it, nopony was around, but there was a letter on the ground. A confession. It described the poison, said that the princesses were affected, and suggested the moon falling was a fearful overreaction from you two. Whoever left it either felt bad, or didn't expect to cause armageddon. And they basically asked me to fix it."
"How did you fix it?"
"We all went to the tree of harmony to get the elements. Turns out they can not only vanquish Nightmare Moon, but fix a nightmare moon." Twilight giggled, but nopony else was impressed. "Ahem... Anyway, sounds like the elements stopped the two of you when you tried to interfere. And also removed the effects of the poison."
"That is all very well, but it still leaves the question of who would have done this. Who could have done this?"
Twilight shrugged. "I don't know, but you should definitely be careful about what you eat. At least until we find out who was responsible. We'll ask the chefs if they saw anything strange and go from there, I guess."
Rarity looked about ready to explode from excitement. She loved detective work.
"Wait a second..." Celestia said, eyes narrow. Suddenly, all attention was on her. "The poison. It was only in the cake, you say?" Twilight nodded.
"Then that could only mean one thing," Celestia continued. Everypony leaned forward. She glared at her sister. "Luna! You ate some of my cake!"
Many miles away, deep in the forest, the former changeling queen, Chrysalis, sat on her haunches, eyes wide and heart hammering.
"Well. Not doing that again."