It was late night when Princess Celestia returned with her sister to Canterlot castle together, once again after one thousand years yet as she closed the door which belonged to Luna's room a troubled look appeared on her face. She placed one of her hoof on the door then lowered her head. She turned around slowly, heading to the other room which got occupied this day.
One of the happiest day of her long life, finally to be reunited with her sister, but she has to try it, even if it looks impossible. Celestia was heading downward into one of the deepest part of the castle where their another new guest is staying.
Couple of tourches on the side of the wall perfectly lit it up to the very end where Celestia stopped in front of the room which was magically protected. She opened the door then entered into the room. It was just like any other normal room in the castle, but it's special guest had to be treated this way for everypony's sake, at least for a while. After a couple of steps, she stopped, closed the door then recreated the barrier.
The pony faced with Celestia, looking into her eyes for a minute then turned away, Celestia lowered her head.
"I'm sorry."
Celestia's voice was soft as always, but sadness covered it.
"I doubt that."
"You two left me no choice, what else could I've done?!."
The last couple of words of Celestia was filled with anger and sorrow. By the time when the other pony in the room turned around to take a look at Celestia who was staring at her while small tears made a pool under her eyes. She opened her mouth for a second, but closed it without saying a word then once again turned away from Celestia, laid down on the bed and closed her eyes. Celestia stepped closer to the bed.
"Fine, but we will have this conversation whether you like it or not."
Before Celestia left the room she turned around to take a look at the back of the alicorn who had her eyes open now. On her way to the throne room Celestia forced a smile on her face. No matter how hard she wanted to end the nightmare forever, she couldn't. She could never kill anypony, not even if it's the pony who ruined her relationship with Luna, who made both of them suffer for a thousand years.
She is part of Luna after all it was her who made her, Nightmare was borned from Luna's loneliness, anger and hatred. Hatred towards Celestia, but she wasn't like that all the time, something changed her, Celestia remembered times when the three of them had fun together, sure after she found out what Luna did, she was furios, but in time she accepted her as her sister, but from one night to another things changed.
For some reason she returned to Luna's body and transformed it into something else and her as well, but when Nightmare was laying in front of Celestia, she couldn't do it, she couldn't end the nightmare once and for all, especially after she saw tears escaping from her eyes, a small hope appeared inside her and brought her back to the castle.
The night passed faster than ever in the last thousand years for Celestia. She was looking at the moon for a bit while before raising the sun then turned to the kitchen to have a breakfast finally with her sister along her side. An hour passed, but Luna didn't show up. She knocked a couple of times on the wooden door.
"Luna?"
Celestia waited a minute, but she could feel her sister is awake and she is inside.
"Is there something wrong?"
The door opened in front of Celestia and she took a couple of steps inside to see her sister is laying on her bed. The pillow beneath her head was wet from her tears which were still leaving her eyes. Celestia closed the door behind herself, laid down next to Luna and cuddled her. It took Luna a few more minutes to stop crying and calm herself, but she still didn't want to face with Celestia.
"I'm so sorry."
"Luna."
Luna turned around and dug herself deeply into the white alicorn's fur.
"I'm so sorry Tia."
Once again she started crying, letting her tears out. Celestia tightened the hug around her little sister.
"I was so foolish and we did things I'm not proud of, I never will be. We fooled ourselves, both of us, to believe something what only existed in our heads."
"Shh, Luna, it's all behind us now, let's go grab something to eat, I'm sure you are hungry."
Celestia got out from the bed, turned around to offer a hoof to her sister who gladly took it after a short hesitation and a smile appeared on both of their faces. While they were walking along each other's side an uneasiness began to build up inside Luna, but she didn't say anything about it.
A month passed, Celestia was spending most of her time with her sister, they were trying to get back the time what they spent apart yet, whenever she could Celestia paid a visit to Nightmare whose existance was covered even in front of Luna who didn't want to talk about it. Most of the times they were only looking at each other without words since anytime when Celestia asked anything, Nightmare never gave an answer.
Celestia and Luna were sitting on Luna's bed, eating, when another letter arrived from Twilight. Celestia placed the food back on the plate and opened the letter. She started to read it while Luna gulped the food.
"She must be annoying."
After she finished reading the letter Celestia let out a small giggle then turned to her sister.
"She is awfully reminding me at you, a lot, her hunger for knowledge, love for the night and plenty of other things as well, you should get to know her, I'm sure you two would get along pretty well."
Luna crawled out from the bed then walked out to the balcony so she can take a look at the night sky. As she walked out Celestia could recognize the anger on Luna's face so she followed her. Before Celestia could place a hoof on her sister's back or say anything, Luna preceded her.
"I don't care, I don't care about anypony."
She turned around to look into Celestia's eyes, only for a second, she wanted to continue, but she couldn't so she turned away.
"Luna, you can't be serious."
"No, I mean, yes I'm. We've been like this before, then we grew apart by time."
Luna looked into Celestia's eyes once again.
"In the end we barely saw or talked to each other,"
Tears began to run down on her cheeks as she spoke.
"everytime when I tried to speak with you during the day, you sent me away because you had duties, you have always found a reason to not to have a talk with me. After years passed, we only met on the balcony where we changed the moon and the sun. You left me alone in the dark, that's why I needed her, she was always there when you weren't."
She laid down on the cold stone and a couple of seconds later she could feel Celestia's warm body wrapping around her own.
"I'm sorry Luna, you don't know how much I'm, but it's not true and you know it. You sealed yourself away from everypony else because you were afraid, afraid of loosing those who were close to you, in time. Twilight would,"
She turned her head around to look into Celestia's eyes.
"Stop it, you should go, you've already wasted enough time on me."
"Luna."
The small alicorn tried to stand up and walk away, but her sister held her down.
"Alright, as you wish, but let me ask you one thing, don't seal yourself away for eternity. Twilight was doing the same as you, living in the dark, so she would understand what you went through, probably more than I ever did, good night Luna."
After a short nuzzle, Celestia stood up and walked away leaving her sister there who stayed behind looking at the night sky. Celestia ordered the guards to close down the throne room and don't let anypony in. She needed to talk with Nightmare, hoping, maybe she can convince Luna, but no matter how many times she visited her, Nightmare never said anything.
Everytime when Celestia stepped inside the room Nightmare was laying on her bed, facing with the wall. She was nothing more than a single idea, an idea what formed a body and came alive. Celestia sat down looking at the other alicorn. Hours passed in silence and none of them even moved. Almost four long hours passed when Nightmare finally had enough of it and turned around to look at Celestia.
"What do you want?"
She slowly raised her head to look at Nightmare.
"To talk about Luna."
Nightmare turned away and let out a sigh.
"Go away."