Heartbreak was the best word to describe it. But it wasn't strong enough.

Celestia had gotten no sleep the prior night. She barely possessed the strength she needed to raise the sun, though it wasn't the physical pain holding her back. Her coat remained dull and ruffled, the skin beneath covered in scrapes and light bruises. Her wings had lost several feathers and one had a large cut beneath it, though the cut wasn't too deep to heal on its own. She hadn't bothered to seek medical attention because, to her, the injuries meant nothing. In comparison to the grief, the physical pain hurt no more than a skinned knee.

She finally stopped crying, only because she became too dehydrated and her throat too sore to continue. Her pillow and the fur on her face were soaked, and her beautiful eyes were red and irritated from rubbing them too much. It was the first time the sun's light was bothersome. She was supposed to go out to greet the public, but today, she couldn't do it. She wanted to be left alone by everypony. Well, almost everypony. But that one pony she'd do anything to have "bother" her... To talk to her, lie by her side, even just playfully poke her in the head...

That pony was gone.

It was a painfully ironic twist of fate. Though ruling a kingdom was far from easy, the exchange of endless appreciation and attention she received from her subjects outweighed the difficulty for her. She never planned to be in the spotlight, but frequent tastes of it almost made it akin to a drug. She enjoyed it. She reveled in it. She couldn't get enough of it. At least, that's what she thought. Little had she known there'd be a high price to pay for it. She thought she'd always seen to it everypony in her kingdom was taken care of. But only recently did she discover there was one she always overlooked. Not on purpose by any means, but lack of intention didn't change the truth of her actions.

Exhaustion finally overcame her and let her sleep, though she was not getting off the hook with a peaceful slumber. It'd be a long time before she got that privilege again.

"How could you?" Celestia looked all around, but she could see no one else there. "How could you?"

"I... I didn't have a choice," Celestia squeaked out. "I had to do it!"

"Did you? Did you really?"

"She was... She was going to-!" Suddenly, Celestia couldn't speak anymore. She couldn't open her mouth.

"Did you really have to do it? Did you try? Did you try to save her? Did you really do everything you could?"

Celestia closed her eyes and trembled, struggling to remain standing as the weight of the truth felt like it was threatening to crush her. When she re-opened them, the speaker had finally come into view. A teenaged pony with a pink mane and tail stood angrily in front of her, gazing at her with piercing fury. A younger filly, boring a light blue coat and lighter blue hair, sat directly beneath her, fearful eyes full of tears as she clung to the older pony's leg. The older pony stood firmly and protectively over the younger one as she continued speaking to Celestia.

"My... my sister..." Celestia mumbled through her closed mouth, but the pink-haired pony understood and, somehow, her gaze became more piercing.

"Don't you dare say that word!"

Celestia's knees wobbled, threatening to give out, but she used whatever strength she could muster to stay upright. Not that it was much.

"You knew it," the pink-haired pony seethed. "You knew something was wrong. You knew she was slipping away. You knew it the whole time. She was hurting. She needed you."

Every word felt like a tiny stab to Celestia's heart. She didn't know if she could endure any more. But she had no choice. It was the truth. She couldn't deny it, no matter how much she would've liked to.

"You didn't listen. You didn't care. She came to you. You turned her away. You heard her cries. You watched her withdraw. You saw her slowly begin to disappear. And you did nothing!"

Celestia tried to force her mouth open to respond, but all that came out were mumbles through her teeth.

"You favored the limelight. You chose it over her. One time. Only one time would you have had to put her first. To talk to her. Remind her you love her. That she wasn't alone. Hug her. Hold her tight. But one time was too much for you."

Celestia finally collapsed to her knees. She would've cried, but no tears came out.

"How dare you! You did not act as a sister should. You don't deserve the privilege of being a sister."

Finally, her mouth could move and she was able to speak. "Please! I love her! I didn't want this to happen! I want her back!"

"Then, why didn't you tell her?!" Celestia shuddered at the fury in the pony's voice. "Why did you let her believe you didn't love her? Why did you never remind her there was at least one pony who loved her, who noticed all her efforts? You had your chances. So many chances to save her. And you failed! You failed as an older sister!"

Celestia looked at the filly, who remained quiet this whole time, but whose eyes had still been fixated on Celestia. "Luna..." Celestia reached out one hoof, but the filly hid her face as the older pony shielded her from view. "Please... I... I would do anything..."

"Why now? Why not before? Why did you neglect her? Are you happy without her?"

"No!"

"Then, why did you behave so? Why was she the only pony you disregarded? She trusted you. Trusted you'd be there for her. But she was misguided."

"No! No!"

"Then, why?!" The pony's tone was loud and enraged. "Answer me!"

Celestia woke up, hyperventilating briefly before sitting up to realize she was still in her room and alone. A dream. It'd only been a dream. Yet, that was somehow no comfort. Somehow finding some strength, she stood and exited her bedroom. The sun shone into the castle's huge windows, beautifully illuminating its halls. But her gaze only met the floor. It wasn't until she reached where she wanted to go that she finally looked up: Luna's room.

She peered in. She should've seen Luna in that bed, sleeping off the tiredness from her nightly duties. Luna had a rather dark taste in decor, but only now did it become haunting. When she thought about it, she couldn't recall Luna sleeping for a full day unless she'd come under the weather. She only ever saw Luna sleeping as she happened to pass by, but it was a brief moment she yearned to have back.

She remembered.

"Celestia?"

"What is it, Luna?"

"Can I ask something of you?"

"Later. I'm busy."

"But you told me that earlier."

"I'm still busy. Don't you have something to occupy yourself with?"

(Days later...)

"Celestia, I wanted to ask if you-"

"Not now, Luna! I don't have time today."

"Why do you always ignore me?! Am I that unimportant to you?!"

"Luna, don't say stupid things. We can talk when I have time."

"You never have time!"

"Luna, not now! Why don't you go to your room if you're so upset?"

It'd been a lie. She was never that busy. She didn't want to deal with it. She assumed whatever Luna was upset about would pass. When that didn't happen, she wanted to believe it was no more than Luna being selfish. She didn't want to believe it was anything more than silly sibling rivalry or Luna was going through some kind of phase. How foolish.

She remembered their childhood. As many younger siblings do, Luna had looked up to her. Initially, Celestia hadn't liked the idea of being an older sibling, but what child ever did at first? It was one night when Luna was a baby that Celestia began to feel differently. That night, Luna had woken up crying. With their rooms next to each other, her cries woke Celestia, who was instantly annoyed, but couldn't return to sleep.

"Mother! Father! The baby is crying!"

When she didn't hear either of their parents coming within the next minute, Celestia gave in and went to try to calm her. She smelled fine. Celestia got a bottle for her, but Luna wouldn't take it. Celestia tried to tickle her and make faces, but none of it calmed her.

"Oh! What do you want?"

Celestia picked Luna up, put her on her back, and walked around in a circle. Luna calmed a little, but still made sputtered wails. Celestia carried her over to the window, where the full moon was in view, shining with all its brilliance. Celestia held Luna in her hooves and she only cried for a few moments more before she stopped and looked upwards toward it. She reached out her little hooves, as if wanting to grab it.

"You like the moon, huh? I like it too."

Luna looked up at Celestia after she said that and snuggled into her. Celestia, relieved she seemed to be going back to sleep, moved her face closer to look at Luna's eyes. Luna grabbed her face and giggled, and still tried to reach for it when she moved her face away.

"Come on. Go back to sleep now."

Luna yawned and stretched briefly, though her eyes didn't close fully. She looked at Celestia again, who had a small, surprised look on her face.

"You can understand me? No, you're too little. Mother says you can't understand us yet."

But Luna wouldn't stop looking at her, and laughed again when Celestia brought her face close enough a second time for her to grab. Celestia carried her back to her cradle, but when she placed her down, Luna started to cry again.

"I'm here! I'm here!"

She picked her up again and Luna quieted almost instantly. Celestia rocked her for a while until she finally fell asleep. By then, Celestia was smiling and didn't want to put her down.

"I guess you're kind of cute, Luna."

Celestia learned later her parents had come, but she was already trying to calm Luna when they came, so they watched to see what would happen. As a child, she was mad at them for that bit of smugness, but from that night on, Celestia only continued to grow into her role as a big sister. Eventually, she'd become proud of it. She taught Luna to say their names. She could calm Luna's tantrums by letting her play and chew on her mane. Sometimes, Luna cried just because she wanted Celestia to hold her. She wouldn't have admitted it back then, if only for not wanting to say her parents were right, but being an older sister had become a source of pride for her.

It was after they became Equestria's rulers it all began to change and sisterhood took a backseat to royal duties. To an extent, it was inevitable, but to go this far was inexcusable. She didn't want to admit it. She didn't want to face they were growing apart. In the end, she failed to do the one thing older siblings were supposed to do: protect. She exchanged being a sister for being a ruler. But she would still pay for that denial. She would pay for a very long time.

All at once, her thoughts turned grim and she found herself close to falling to her knees again. Only a few tears managed to roll down her face, but the grief couldn't be more evident.

"I don't deserve to call myself a sister. I don't deserve you, Luna. I don't deserve to be your sister."

Author's note: I cannot stop writing about these two, but I realized all my stories of them so far are happy ones. I wanted to write a sad one, and the Nightmare Moon history is really perfect for that. To clarify some things, I know as far as canon goes, Luna was jealous and nothing more, but my personal theory is somewhere between taking Equestria's throne and Luna becoming Nightmare Moon, their relationship began to fall apart. After all, if they were close all throughout that time, they could've talked about it long before Luna reached her breaking point. Sure, close relationships don't prevent jealousy, but there'd be the question of why Celestia ignored Luna in the first place or why Luna never went to her if they were really best friends at that time. And I'm not buying something along the lines of Luna was jealous for a month before she went crazy. I know this is a fictional show, but that's too far-fetched for even me. The show does support Celestia being a bit naive and impulsive, so I think it's believable she wasn't a good sister back then.