Celestia found a scroll on her desk that morning. She could make out its shape from her bed, even in the dim light of dawn. She must have slept through the dragonfire delivery.
It must be a letter from Twilight, she thought, no doubt discussing her sleepover with Luna last night. Celestia eagerly unfurled it, excited to hear all about her sister's new friendships. Upon reading it, however, she found herself filled with worry.
Celestia rose the sun before heading to breakfast. She needed to talk to her sister.
“Hello, Luna,” Celestia greeted as Luna entered the dining hall. “How are you?”
“Hello, sister,” Luna answered as she closed the door behind her. “I am fine.”
“I received a letter from Twilight.” Luna winced as she spoke the words. Celestia felt a pang in her heart at the sight, but she had to press on. “What happened?”
“I...” Luna stuttered, struggling to find the right words. “I got overwhelmed.” She looked down at the floor, unable to make eye contact. “There were... things I wasn't prepared for.”
“She said you disappeared after going out for some air,” Celestia continued. “Did you fly all the way back here?”
Luna nodded.
“What was it that got you so worked up?”
No answer came. Luna continued to stare at the ground, leaving Celestia confused. Her sister was usually very cooperative, willing to humor her at worst. This gloominess was a side of Luna she hadn't seen before. It made her uncomfortable.
“Luna, please come over here.”
Her sister obeyed, reluctantly placing one hoof in front of the other, as if she were marching to her own funeral. She yelped when Celestia embraced her with a wing.
“Sister mine, please understand,” Celestia said as she wrapped her forelegs around Luna. “I love you more than anything. I care for you deeply. I want you to find happiness, but I can't help you if you don't help me. Please tell me what's wrong.”
To Celestia's shock, Luna started sobbing. Her cries filled the dining hall and quickly smothered Celestia's appetite. She had expected Luna would be upset, but not like this.
She began to gently stroke Luna's mane, unsure of what to do. Eventually, Luna found her voice.
“They didn't work.”
“What didn't work?”
“The Elements. They didn't fix me. She's still here with me.”
“She?” Celestia pulled back to look at Luna. “You mean Nightmare Moon?”
Luna nodded, pulling herself closer to Celestia. “I can hear her voice inside my head. She berates me, manipulates me. She wants me to make that terrible mistake all over again.”
Celestia hugged her sister once again. “Luna, why didn't you tell me?”
“I'm sorry. I didn't think...” she paused to take a breath. “I wasn't thinking. I didn't know what to do. Everyone thought I was fine. I thought I was too.”
Suddenly, Luna lurched in her grip.
“Shut up!” she shouted. “Don't talk to me anymore! You've ruined enough...”
“Luna, please. You're okay. I'm right here.”
“I'm so sorry, Celestia! I'm so sorry!” Luna shouted as she sobbed harder. Her whimpers carried hint of desperation, and she clung to Celestia tighter. ”I'm just so lost, sister! I don't know what to do!”
Cradling her broken sibling, Celestia reconsidered her plans for the future. She had thought Luna was nearly ready to be her own pony again, and find her place in the world. Her dreams of once again ruling beside her sister had seemed so close to fruition. But she couldn't have been more wrong. As long as Nightmare Moon was plaguing her, there's was no hope of Luna's recovery. This was serious.
“Don't worry, Luna,” she whispered in her sister's ear. “I'll stay with you. We'll get through this together. I promise.”
“Princess Celestia! Is everything okay? Is Princess Luna alright?”
Celestia wore her ever serene smile as she watched her student run across the castle hall. Twilight's face, however, was filled with worry.
“My sister is fine for now. She's resting in her room.”
Twilight looked relieved upon hearing that. Celestia realized she had likely spent her entire train ride worrying about what was wrong. Knowing her student, she had probably assumed something catastrophic, like an attack on Equestria. Not that the actual problem wasn't serious, but she still should have been more specific in her letter.
“That's good to hear. But, why did you call for me?”
“I'm very sorry to summon you like this, Twilight,” Celestia started. “You've already done so much for the two of us, I hesitate to ask you for more.”
Twilight put on a confident smile. “Don't worry, Princess. I'm always happy to help.”
Celestia felt her smile widen at Twilight's words. “That's what I thought you'd say. And why I asked for your presence here.” She took a deep breath. “It seems the Elements of Harmony did not work as well as I had thought. While they did return my sister to me, they did not save her like I had hoped.”
Twilight tilted her head in response. Celestia closed her eyes, trying to maintain her calm expression while she found the strength to speak.
“The Nightmare still lurks within Luna's mind.”
Twilight's eyes went wide. “That's why she was whispering to herself,” she thought aloud. Then she shook her head, trying to stay focused. “Has she been that way since the Summer Sun Celebration?”
“As far as I know,” Celestia answered.
“Oh no. Poor Luna...”
Celestia resisted the urge to sigh, finding it harder to keep her emotions in check by the second. “I must admit, Twilight. I'm not quite sure what to do in this situation.” She wasn't even sure what to call it. Possession? Infection? Mind control?
“Well, what do we know about Nightmare Moon?” Twilight asked.
“Not much, I'm afraid. Luna and I never really discussed it. I had thought—” Celestia paused as the weight of reality settled in again. Her mask started to slip off her face. “I thought it was over now.”
Celestia must have looked as scattered as she felt, if Twilight's expression was anything to go by. She couldn't maintain her composure when her sister was in terrible danger just a few rooms away. She had spent the last thousand years trying to stop herself from worrying about her sister, focusing instead on her nation. Now that Luna was back, it was much harder to distance herself.
Celestia took another deep breath.
“You raise a good point, my student. Perhaps we should ask Luna how we might best help her.”
“Luna?” came a muffled voice, accompanied by a knock at the door. “May we come in?”
Celestia had said 'we'. That meant Twilight was here. Luna was filled with shame at the thought of being seen like this.
Well? Will you deny them?
“Come in,” Luna answered. She'd rather shame than this torment.
Her sister and the mare who tried to save her entered her chambers. Luna got up from her bed to greet them as they stumbled inside. It took a moment for their eyes to adjust to the darkness of the room, but eventually they found their bearings.
“We're here to help you, sister,” Celestia said. “But we can't do it without you.”
“What do you need from me?”
The two ponies before her shared a worried look
“We need to know more about her, Luna. We need your advice for combating Nightmare Moon.”
Luna felt her heart drop. She honestly should have seen this coming.
Oho! They wish to learn about me! the voice exclaimed. Perhaps you wouldn't mind letting me answer personally? They might appreciate getting answers directly from the horse's mouth.
“What do you want to know?” Luna asked. The voice chuckled inside her mind.
“What exactly is Nightmare Moon, Luna?” Twilight asked.
The voice gasped. So direct! So upfront! it mocked. How in Equestria will you weasel your way out of this one?
Luna's entire body froze on the spot. She couldn't answer that question. She couldn't admit it, not to them of all ponies!
The voice howled with laughter. Finally, forced to face the music! Nowhere left to hide!
It laughed with a type of glee Luna had never heard from it before. Like it thought it was being freed from her. Luna fell to her hindquarters, no longer having the strength to stand.
“Luna, are you alright?” Celestia's voice barely reached her through the chaos.
Don't say I didn't warn you! I knew this day would come! I've been waiting for so long!
“Please... help me,” she said weakly.
“What's wrong? Is it her? Is she doing something?” Celestia and Twilight each took one of her hooves, holding her close as they sat beside her.
The laughter continued to echo in her mind.
“I don't know what to do...”
Celestia felt helpless as she watched her sister spiral down into madness. There was nothing she could do to ease Luna's woes, she could barely even get through to her at this point. With Twilight's help, she lifted her back into bed, sparing her a sorrowful look before walking out the door.
Twilight managed to maintain her composure just long enough for them to leave Luna's chambers. As soon as the door was closed, however, she threw herself at her mentor's hooves.
“I'm sorry, Princess! I didn't mean to hurt her!”
Celestia shook her head. “Please relax, Twilight. You've done nothing wrong.” It was typical of Twilight to panic whenever anything went wrong, but her student wasn't the one responsible for her sister's plight. Celestia helped her to her hooves while she thought about their predicament.
She had been foolish, believing everything would work itself out. The Elements had only created a temporary solution the first time she had used them against Luna, she didn't know why she expected anything different now. It had been so exciting to have her sister back, she had completely forgotten the reasons why Luna had left in the first place.
But how did she fix this? If not with the Elements of Harmony, then what? She wished she could have Luna's help, but what could she ask her to do? Luna had already suffered enough by herself at Nightmare Moon's hooves.
Maybe that was the secret. Luna needed someone else to help her fight. Someone close to her, who knew her well. A pony with a caring nature, who wouldn't falter in the face of adversity. A force of good who could stand against Nightmare Moon and win.
“Twilight, I have an idea.”
Celestia wasn't sure if it was a very good idea, but she didn't exactly have many options at the moment. She certainly couldn't let Luna continue to suffer like this.
“What is it, Princess?” Her student looked up at her, hopeful as ever. It gave Celestia just a bit of confidence.
“I think we might be able to reach Luna through her dreams.”
“Through dreams?” Twilight was stunned. “Can we do that?”
“I certainly can't,” Celestia admitted. “But Luna is very skilled in manipulating dreams. She might be able to let you into her mind through a shared dream.”
“That does sound interesting,” Twilight said. “Wait, me? Just me?”
“I'm sorry, my student. I can't help but feel my presence would only make things worse. I've no doubt Luna cares for me deeply. Nightmare Moon on the other hoof...” Celestia slowly shook her head. “Luna clearly is having a hard enough time as it is. I don't want to agitate Nightmare Moon if I can help it.”
“I... I guess that does make sense...” Twilight didn't sound convinced.
Celestia had to admit she was uncomfortable letting her student share a dream with Nightmare Moon. But she had faced this villain before. She and her friends had already proven it was possible to beat her.
Besides, if there was anypony to send to comfort her sister, it would be Twilight. She was a pony who knew the struggle of making new friends, and of living in Celestia's shadow. Twilight had a made a real connection with her sister and bonded over common ground, instead of merely being related to her by blood.
“Can you do this for me, Twilight?”
“Well, I do want to help Luna...” She looked to Celestia for reassurance. “It's only a dream, right? She can't hurt me through it?”
“Not physically, no,” Celestia answered. “She can only share experiences and thoughts with you. But you have a strong mind, Twilight. I don't think she'll be able to hurt you.”
“Then, yes. I'd be honored to help.”
Twilight's agreement helped ease the dread in Celestia's gut. She was truly blessed to have stumbled across such a faithful student all those years ago.
“Thank you, Twilight. You are truly one of the bravest ponies I've ever met.”
Twilight blushed at the compliment.
“Come with me. Let's get you ready.”
The door to her chambers opened slightly, a sliver of light shinning through the gap.
"Luna?" called Celestia's voice, gentle and concerned. The sound made Luna's heart jump in her chest.
"Sister?" she timidly answered. Celestia was certainly here to ask her about Nightmare again, but Luna had even less strength to face that now than she had a few hours ago.
"I had an idea to help you," Celestia said, making her way inside. "Clearly Nightmare Moon is causing you a lot of trouble, but there's not much Twilight and I can do to help you if she's inside your mind. So, I thought you could make one of those shared dreams like you used to. You could share it with Twilight, and she might be able to help you face her again."
That... was an interesting idea. Twilight certainly knew how to handle Nightmare Moon, of that Luna had no doubt. Maybe she really could help her.
Sounds like fun! Go ahead, invite her in.
The voice's optimism gave her second thoughts. Surely it wouldn't be so happy to hear this if it didn't have a plan. But then, what could it possibly hope to do to Twilight in a dream?
"I can do that," she said to Celestia. "Just Twilight?"
"Just Twilight," Celestia confirmed. "I figured Nightmare Moon would be far more tolerant of her than of me."
Luna felt a strange sense of relief on hearing that. Something about the thought of sharing a dream with Celestia made her uncomfortable. Giving her sister a chance to see her deepest thoughts just seemed like a recipe for disaster.
"Very well. I'll search for her when she falls asleep."
Celestia smiled. "Thank you, Luna." She lifted a hoof towards Luna's bed, before awkwardly putting it back down. She gently shook her head, an act she probably thought was invisible in the darkness, but that Luna had no trouble noticing.
"With Twilight by your side, I know you can overcome this," she said instead. "You're strong ponies, both of you. You'll be alright." With that she made her way back to the door. "Good night, Luna."
"Good night, Celestia," Luna replied. The door shut and Luna was alone once again. There was no time to dwell on her sister's strange behavior. She had a dream to create, and a very important mare to link to it.