Every pony knows about Luna and her reign of terror amongst the ponies of Equestria. Being the Princess of the night when all the ponies slept and never enjoyed her beautiful moonlight, and all of them would attend the raising of the sun each morning but never held such events when it was time to raise the moon. After years of being hidden from the eyes of the public and begging for another hour or two, Luna took it upon herself to prevent the sun from ever reaching the sky. The mutiny was short lived, being ended by Celestia and her Elements of Harmony which locked Luna away in the moon for one thousand years. One the one thousandth day Luna escaped from her prison and once again tried to overthrow Celestia and was once again defeated by the new wielders of the Elements of Harmony. Luna begged for her sister's forgiveness when she was defeated a second time and Celestia agreed to allow Luna to rule the night yet again. Almost four years have passed since Luna had been ruling the night and times had certainly changed since she was banished. Ponies were out and about at night whether it was work related or for recreation; it was a little more pleasant to endure although it still wasn't nearly as pleasant as ruling the sun, but Celestia did implement the Sunlight Savings Cycle which allowed Luna to have more nighttime during the winter hours when crops couldn't be grown and snow made daily activities a little too dangerous. Luna got almost fifteen hours of nighttime out of this which was three hours more than what it normally would be during the summer season.
There was one thing Luna never knew the answer to but was itching to know. How did Celestia feel about what had happened all those years ago? Was she happy? Was she sad? Are there any regrets? Celestia didn't apologize for any of it which Luna half expected given the way she tried to overrule her, but she also never said anything about it all since Luna had returned.
Luna walked into the common area of the Palace where she found her sister asleep on a couch along with a few scrolls, some of which were rolled out and others which were still rolled up with red ribbons securing them. One was rolled out just ahead of Celestia's nose where she had been laying. Luna walked closer to the letter and saw in the blank area underneath the message were a few wet spots which looked like they hadn't been there for too long. Luna's own eyes began to tear up as she recalled the events one thousand years ago. A few moments after her thoughts her horn began to glow which brought up a transparent cloud above Celestia's head which revealed an image of her and her sister, both young and in the palace. Celestia was seated at her throne while Luna was standing before her on the red carpet; she was dreaming of that faithful day which ripped their own sisterly friendship apart. Luna thought long and hard about entering this dream. One one hoof she desperately wanted to know what her sister was thinking and how she reacted but, on the other hoof her sister probably hadn't mentioned anything for a reason. Curiosity got the better of the Princess of the Night and she climbed into the dream cloud.
Luna was standing behind her younger self, keeping herself hidden from Celestia's view with a spell that wouldn't let her appear in a dream unless she wanted to. Luna watched as the two sisters talked amongst themselves.
"Celestia, please," Young Luna begged "I'm just asking for one more hour of night. It won't do any harm to any pony."
Young Celestia rolled her eyes.
"How many times do I have to explain this to you Luna," She asked angrily "We can't have any more hours of the night than we already have because the crops won't be able to grow as efficiently. If the ponies can't grow crops and then they starve. Would you rather have that!?"
Young Luna turned her head away with tears in her eyes.
"I don't think one extra hour is going to harm the crops," she said "You have fourteen hours of daytime and I only get ten hours of night. It's not fair!"
"Life isn't fair Luna," Young Celestia snapped angrily "I'm done with this conversation! Now get out of her before I strip you of your duty!"
Young Luna gasped at Celestia's remark and walked out of the room. Her eyes filled with tears and as upset as she would ever be. Luna already knew what happens to her, she walks out and becomes Nightmare Moon a few hours earlier and gets defeated; she decided to stay with Young Celestia and see what happens.
The dream flash forwarded to a few years after she was banished. Young Celestia was laying in her bed underneath the covers; Luna was on the other side of the room but flew over the bed where she cast another dream spell that let her see underneath the covers. Young Celestia was hysterically crying while clutching a picture of herself and her younger sister in front of the palace. They were both smiling and had their wings wrapped around each other which Luna was able to determine was taken the day after they were inaugurated as rulers of the land.
"Luna! Luna," Young Celestia called out "I'm sorry Luna!"
The words Luna had wanted to hear for the last four years. The apology she longed for after the apocalyptic battle that could have ended with their own deaths, the answer she had been looking for for the last one thousand four years.
"I've tried so hard to counter the spell but I can't do it," Young Celestia cried "I didn't want it to be this way."
Luna herself had begun to cry. She wanted to hear Celestia's apology but this was too much for her to handle.
"I promise I'll give you more night. Please just come back to me," Celestia begged as more tears dropped onto the picture "Please!"
The dream ended a few moments later but Celestia was still asleep; presumably in another dream. Luna's eyes were filled with tears as she took in what she had seen. Luna's time away was filled with anger, hostility, and vengeance; Celestia's time away was filled with sorrow, pity, and distress. Luna rubbed her hoof along Celestia's back softly as she saw tears coming from her sister's eyes.
"Sister," Luna said softly "It has been so long since that time. I've forgiven you for your mistakes as you have forgiven me for mine."
A tear dropped from Luna's eyes and onto one of Celestia's wings; she continued to rub her back gently.
"But please, please Celestia," Luna said "Forgive yourself."
Luna lowered her head as retracted her hoof, ready to leave. At that moment Celestia quickly sat up and hugged her sister as tight as she could, tears filling her eyes.
"I'm so sorry!" She cried.
Luna returned the hug and rested her head on Celestia's shoulder.
"Oh Celestia." Luna said softly.
"There isn't enough I can possibly say or do to make up for what I did. One thousand years I'll never be able to take back, and it's all my fault!" Celestia said.
Luna pulled away and looked into Celestia's eyes.
"No...it's not," Luna said as she wiped her sister's tears away "We both made mistakes and we both paid the price for them. We were very young."
"Every," Celestia said as she began to cry again "Day."
Luna hugged her sister once more.
"I know."
The two sisters looked at each other once more and smiled, tears still in their eyes. All those feelings locked away in Celestia's heart had finally been released to Luna, the answer she so desperately longed for all those years of being imprisoned in the moon.
"You should get some sleep sister," Luna said "Only a few more hours left of nighttime."
Celestia smiled and laid back down on the couch. Luna wasn't sure why she didn't walk up to her bedroom but it didn't really matter. What mattered is that the two of them finally were able to speak about what had happened and it seemed to be just as relieving for Celestia as it was for Luna. Celestia has once again fell asleep next to the letter she had read just before she had fell asleep a few hours ago.
Dear Princess Celestia
Today I learned that friendship is all about compromise. In order to have a successful friendship you have to be willing to compromise in a way in which all parties will be satisfied. Every pony wants everything to be their way and there will always be differences between themselves and their friends, but you can't always have your way all of the time. One small sacrifice is worth the friendships that you will gain, and failing to agree on common grounds can tear friendships apart without knowing if the damage caused can ever be repaired. I'm just glad I was able to learn this over something small rather than something that could cause harm to more than just the two of us.
Your faithful student,
Twilight Sparkle