After the party ended, and Celestia and Luna thanked everypony for coming as they saw them out, Luna decided to nap for an hour before she began her nightly patrol of the dream realm. She had an amazing time at the party, and an amazing birthday as a whole, but being a little on the introverted side, all the social activity had worn her out. Not that every ounce of the exhaustion, and the stomachache from eating so much cake, hadn't been worth it.
Luna woke up, and stretched out her legs and wings. She looked outside at the night sky. The stars were no longer twinkling, yet in Luna's eyes, they were somehow still shining more brightly than other nights.
"Sister, are you awake?" Luna heard from the other side of her bedroom doors.
"Please come in," Luna replied, turning to face the door as Celestia entered.
"Seems I caught you just in time. I wanted to speak to you for a moment before you leave for the dream realm."
"Anything," Luna said.
Celestia closed the door, ensuring the sisters' privacy. They lied near Luna's bed.
"I didn't want to mention this at the party," Celestia began. "I'm sure I know the answer, but just to hear it from you: why did you never ask for a throne to begin with?"
Luna frowned. "For the same reason I didn't acknowledge my birthday until the little ones spoke of it. I did not feel I was worthy of it. I did not feel I had the right to request anything, especially from you, let alone request a throne for myself. Even if that were not the case, I still had much to learn about the modern world and I must admit I am still overwhelmed by the vast changes. I am unsure I can fully educate myself about a thousand years of changes."
"I thought so," Celestia sighed. "Sister, first, please don't worry about that. I couldn't recall a thousand years' worth of history for the sake of my life. You needn't push yourself so hard over that."
Luna grinned for a second.
"More importantly, I suspected as such. There was a reason I arranged this celebration for you."
"Yes, you said so," Luna recalled. "You felt you should've had a throne waiting for me upon my return. But, really, it's---"
"Not okay," Celestia cut her off. "It is not okay, Luna. When you returned, I was so happy to see you again, so eager for you to come back to me, so hopeful for things to return to how they were... I was so focused on what I wanted, I forgot about you."
"Sister, I apologize, but I fail to understand what you attempt to explain."
"I made the same mistake I did in the past," Celestia lamented. "I didn't mind your negative feelings growing, assuming they'd pass on their own. When you returned, I didn't mind - rather, I didn't consider - the effects you were suffering from your time in the moon. I knew you were physically unwell for a while, but the mental and emotional toll never crossed my mind."
Luna stayed silent.
"You said Nightmare Moon overtook you. You had no free will, but you knew what was going on. So, you knew the time was passing. You were conscious for every second of your isolation, weren't you?"
Luna shuddered and looked away, but that response answered the question.
"Yes, and I foolishly failed to consider what a thousand years of isolation could do to a pony," Celestia continued.
"You are not omnipotent!" Luna interjected, desperate to alleviate her sister's guilt.
Celestia shook her head. "I don't need to be. It should've crossed my mind. In our modern world, solitary confinement is considered torture, Luna, and I am the one who wrote that law. There's no reason I shouldn't have thought about that. Your celebration and throne were not only birthday gifts." Celestia pulled over a mirror from the corner of Luna's room and set it in front of them. "They were meant as a reminder."
"A reminder of what?" Luna asked, watching her and her sister's reflections in the mirror as Celestia was doing.
"That you are also a princess."
"I have never forgotten that."
"Are you positive?" Celestia asked. "When I tried to talk to you about taking up your duties after you recovered, you called yourself a monster. You created a monster for the sake of tormenting yourself. You were really determined to never let yourself move on from what happened. Nothing you did - bringing our peaceful night, guarding our dreams, giving ponies guidance when needed - was enough for you to believe you weren't a monster."
"You could forgive yourself for attempted murder?" Luna asked, now staring at the floor.
"About that..."
"Yes?"
"You do know that battle raged only for about five minutes, correct?"
"I am puzzled again, sister," Luna replied, now making eye contact with Celestia.
"It was awful, yes, but you barely did me any harm," Celestia explained. "The castle had more damage. You knocked me out for a minute or two and I hit the ground. Besides a bit of a headache, the pain was over when I woke up and I had nary a scratch."
"You don't have to minimize what happened," Luna insisted.
"I'm not. I am being truthful. I know it was an attempt to end me, but I was unharmed. I don't believe Nightmare Moon could utilize your magic properly."
Luna's face still held its puzzled look. "What did I hit you with, if that is the case?"
"Maybe just a standard beam or a stun spell. I presume the fall was supposed to be my demise."
"I am glad to know I did not harm you greatly, but that outcome does not change my intent."
"What I'm trying to say is it's unimportant now," Celestia said, returning to the subject of the party. "The celebration and the throne were for you to finally see and acknowledge yourself as the princess you are. That's what I hoped for. You are my equal, and you need to believe that. You have the same power and authority as myself, Cadance, and Twilight. As Equestria's monarchs, we should converse about big decisions, of course, but you don't need to wait on me to give yourself anything."
Luna blushed. "If you knew how I initially handled Nightmare Night, you would dethrone me immediately."
"Because you impulsively banned Nightmare Night because of its meaning and were hurt everypony continued to fear you?"
Luna's eyes widened in shock.
"Twilight gave me a rundown of the events in a separate letter." Celestia shrugged. "Hardly the worst thing. Nopony is perfect. I mistakenly ruined Twilight's former friendships that I never knew she had and was a poor mentor to a student I had before Twilight. I could write and publish a book titled 1,000 Things You Shouldn't Do When You're A Princess."
"I would read a book titled such," Luna laughed.
Celestia smiled. "You never stopped being our princess. To minimize the good you do is as bad as to exaggerate it. You are a splendid princess, and more than that. All of our little ponies have come around and accepted you. If you had thought to have a throne for yourself, I wouldn't have objected if you attained it without my input. I'd be curious you never mentioned it, but not against it. So, is it possible, my sister? Can that awful time of the past be left in the dust? Can I see my lovely sister on her throne, holding herself proudly as our princess of the night?"
Luna beamed and her smile stayed. She thought back to the wish she made on her candles.
"Yes, you can. You are a remarkable sister. I love you."
"I love you too."
The sisters nuzzled each other briefly, but Luna jerked away and her eyes glowed white. She began to strain herself and her body struggled uncomfortably.
"Luna! Luna, what's wrong?" Celestia cried as she grabbed her younger sister. Luna didn't know what was happening to her, but she also grabbed hold of Celestia, and the two held on to each other until Luna's body flashed a black color. Suddenly, standing right before them was a translucent image of Nightmare Moon, who roared before disintegrating into the air. Luna's eyes returned to normal and she let go of her sister.
"What happened?" she asked as she regained her breath. "What was that sound?"
"Nightmare Moon came out of you," Celestia answered, much to Luna's horror. "But she vanished."
"Vanished?"
"She appeared from you, roared at us, and disappeared like dust into thin air."
"So, it really is gone," Luna mumbled.
"What do you mean?" Celestia asked.
"When Twilight Sparkle and her friends purged me of Nightmare Moon years ago, the elements did not truly remove the darkness. It would be more accurate to say they reversed it."
"Reversed it?"
"The darkness shrunk to its smallest point, when it first came into my heart from my emotions of jealousy and resentment."
"So, all this time, you've had the propensity to transform into Nightmare Moon again. But why did you fear that?"
"Darkness grows from hate, sister. Any kind of hate."
"Any kind of hate..." Celestia mumbled. "Your self-hate! You feared Nightmare Moon returning because of your self-hate? What about the tantabus?"
"I created the tantabus to give myself nightmares and to prevent Nightmare Moon's rebirth," Luna clarified. "I attempted to confine her to my dreams. But if she vanished as you say happened just now, her darkness is truly no longer existent. It is gone."
Celestia looked into the mirror again. "Then, who's in the mirror with me?" she asked with a grin.
Luna stared and smiled too. "Equestria's princess of the night."
"And her name is?"
"Princess Luna."
Celestia placed her hoof across Luna's back. "Don't you ever believe yourself to be any less. You are worthy, Luna. You are a wonderful princess. And sister."
"I think I can believe that."