"Dear Princess Cadence,
I hope this letter finds you well. I promised at our last meeting, that I would tell you more about our situation, so I have written this missive to summarize the details.
"As you know, my sister rebelled against me one thousand years ago, and in a last-ditch effort to save my life, I used the elements of harmony to banish her to the moon. Because I stole control of Luna's elements and used them against her, they rejected me as a bearer, and I am left with no defense against my corrupted sister.
"I had long since hoped that Sunset could be a bearer of the element of magic, but you now know why that is not the case. Only an Alicorn can wield more than one element at a time, and I hope that you, dear Cadence, can become the bearer of kindness, generosity, and magic.
"That sixth element is the most powerful and tricky. It requires both an abundance of magical reserve (which you have, since your ascension), and friendship toward others. Normally, I would suggest that you were more suited to have honesty as a third element, but the artifacts are unlikely to work, if magic is not activated first.
"While it is possible that you might be a suitable bearer for all six, it isn't advised. I last used all the elements at once, when Lulu was banished, and it nearly killed me. I believe that when Nightmare Moon returns, control of three elements by a new Alicorn will be enough to coerce her into a stalemate.
"While it is not the ideal outcome, we may still be forced into battle. If that comes to pass, you will need to lend me your power. The magic-sharing spell is attached below. The Everfree forest was the result of our last fight, and the primary reason I wish to avoid combat this time around. What used to be a normal forest around our castle, grew into a dense jungle, whose magic worked on its own and attracted many dangerous creatures within its boundaries.
"I am truly sorry for dragging you into this, my lovely niece, for ever since you appeared, you have been my steadfast student and the heir I always wanted. But at last, I have no choice but to rely on your support. My student is gone, my connection to the elements is gone, and we are a scarce three years from the thousandth Summer Sun Celebration.
"With much love and trust, Princess Celestia."
* * *
Moondancer was not a patient mare, as was evidenced by the rut she was wearing into the floor as she paced in circles.
"Um, Moondancer? Are you okay?" Spike asked, following her route with his little claws.
"No Spike, I'm not okay!" The unicorn all but growled at her little assistant, and he flinched away from her. That made the mare a little guilty, and she wrapped Spike in a hug.
"Think about it this way, Spike. I have definitive proof that Nightmare Moon is returning, and the Princess won't trust me enough to send help!" Moondancer groaned and bit her lip.
"I get it." Spike nodded. "It's not just about you, you feel like you're hurting all the people you could save if they only knew."
"Right. But what can I do, if the Princess just won't listen?" She frowned, and plopped down on the floor.
"Maybe, just... listen to her?" Spike suggested. "I mean, if Princess Celestia doesn't think it's a problem, why should you?"
"Because it isn't the first time she's been wrong about something." The cream-coated unicorn noted, sniffling a bit.
"Is this about your grant project?" Spike asked, and received a nod in return.
"We can use magic and science together, to do so much good for the nation!" Moondancer practically spat, anger coloring her very posture. "If it weren't for those nobles, and their refusal to pay for things that don't make money, I could make leaps and bounds of progress in all sorts of industries!"
"Well why don't you just prove it?" Spike asked, receiving a gasp from his older-sister figure. "Equestria may be behind in technology, and a bit tribalist, but we're in an unprecedented era of peace."
"That's brilliant, Spike! I'll just prove that Nightmare Moon is returning, and then the Princess will have to believe me!" Moondancer bounced in happiness.
"Er, aren't you getting a little carried away?" The drake asked his unicorn, who blatantly ignored him as she flurried through books and scrolls. When he said 'prove it' he didn't really mean 'go hunting for Nightmare Moon'. Also, his fact about unprecedented peace was totally ignored by his older companion.
"According to Clover The Clever's Laws of Banishment, the banished pony can typically only return from the very point where they were magically exiled, which in this case is..." The unicorn prodigy muttered to herself, as she pulled out a map. "Let's see... castle of the two sisters... formerly housed in the Everfree forest... closest settlement..."
Finally, Moondancer grinned.
"Pack your bags, Spike. We're going to Ponyville."
* * *
"Dear Princess Celestia,
You're always telling me to make new friends, and take chances, and learn to relax a little. Now, after the most recent failure of my Magitech proposal, I have finally taken your advice to heart.
"I kindly ask your permission to take a vacation to Ponyville, the most friendly town in Equestria, so that I can put your lessons to good use, and try to make some friends.
"Your most faithful student,
Moondancer."
* * *
Ponyville was a friendly town, to be sure, and it was largely thanks to Princess Celestia's behind-the-scenes chess games that had made it such a good place to be. From the very first settlers, Celestia had made sure the town was populated with all kinds of ponies, a veritable cross-section of the kind of world she envisioned. The first settlers in that town were the Apples. They were a sprawling and talented earth-pony clan, who seemed to sow apple trees and friendliness wherever they went. Attracted by marketable produce, the Rich family came along, one of Equestria's first new-money earth pony families.
The town wasn't far from Cloudsdale, so when enough citizens lived on the ground to pay the weather ponies, Ponyville got a quaint little weather team. The Belle family was a former noble house of Canterlot, and when they asked Celestia where to go, after being evicted from their family manor, she gave them a pouch of bits, and pointed them to Ponyville.
From the very beginning, the Sun Princess had done everything in her power to make that town her hope for the future. For one reason, she wanted ponies of all three tribes to live and work together, with no job segregation, or cruelty. For another reason, the fact remained that friendship was the catalyst for the elements, and so Ponyville was established, publicly as a picture of diversity, and privately, as Celestia's draft pool to find bearers for the elements of harmony. As an added bonus, the town was right up against the Everfree, in perfect position to prepare for the arrival of Luna.
If there's anything left of her inside that monster... Celestia added in her own mind.
While the Princess had the power to make sure there were proper bearers at the right time in the right place, it would be an abuse of her power as a monarch, and there was no guarantee that the elements could be tricked like that. All she could do was make sure the conditions were best, and prepare for the worst. To this day, Celestia was not the strategist her sister was. She could only hope that even the nightmare had a soul, and could be convinced not to come to arms against her good ponies.
With a puff of smoke, a letter materialized through dragon-fire. Celestia looked at it with a smile, once she saw her student's familiar stationary. Moondancer had the knowledge, and an incredible memory, but she didn't have any more magical reserve than a typical unicorn. If unicorns were to be ranked on a scale from one to five, where one represented a foal with barely-realized magical power and five was Starswirl The Bearded, then Moondancer would probably rank as a two. She could levitate objects and cast all kinds of spells, but her magical strength and stamina left much to be desired.
Celestia looked on Moondancer like a mother takes pride in her foal. Orphaned from an early age, she became the Princess' personal student after passing the entrance exam with flying colors. Her only fault, Celestia thought, was that she needed to make some friends.
So the princess took out her quill, and wrote a reply.
"Dearest Moondancer,
I'm so glad that you're taking my advice to heart, and going off to make new friends. I can personally attest to the fact that Ponyville is a wonderful town, and I hope you enjoy your time there. Speaking of time, take as much as you need. There is a vacancy open for a librarian in Ponyville, so if you'd like, you can stop by Mayor Mare's office and ask about it."
"Wishing you only the best of luck,
Princess Celestia."
Was it wrong of her to think that maybe, now that Moondancer was leaving, she could spend more time with Sunburst? Yes, Celestia concluded, the guilty feeling of excitement was most certainly wrong, even if it was simply born from the misguided hope that she could keep some part of Sunset Shimmer near her.
With these feelings of guilt settling on her chest, Celestia hoped that with any luck, Moondancer would find some worthy element bearers in Ponyville.
Little did she know, six ideal bearers, connected by magic and driven by fate, were already half-aware of their status, and working for the other side.
* * *
"Dear Princess Celestia,
"Since your last letter, I've done some reading about the elements of harmony, and I feel compelled to raise some concerns. Firstly, from the few instances in which we've seen the elements in action, how can we draw any conclusions about what might happen to Auntie Luna, should we turn the elements on her in fear?
"These artifacts cannot strictly kill, but think of the handful of times they were used. Your theory is that the elements will not obliterate Nightmare Moon, but purge the chaos and darkness from her very mind. Despite the fact that they are powerful harmonious artifacts, they have never once treated chaotic energy in so merciful a manner. When used on Discord, they turned him to stone. When used on King Sombra, they locked an entire empire of ponies into a shadow prison. Whether this has anything to do with Sombra's own spell work or not, is irrelevant.
"Innocent ponies were hurt, because they got caught in the elements' line of fire. And you want to turn it on an enemy who might still, deep down, be your sister? In the most likely scenario, she'll just be banished again, and a thousand years from now, she'll still be angry with you, Aunt Celestia.
"That said, if your plan is to bluff Nightmare Moon into thinking we'll use the relics against her, I can support you. If you plan to actually use them against her, I must solemnly beg you to reconsider and go over the evidence, such as we have. In regards to your previous instructions, I have learned the power-sharing spell, as you requested.
"Business aside, this part of the letter is directed, not as a subject and princess, but as a niece to her mentor, aunt, and friend. I really, really wish you two would just talk to each other when Luna gets back. You know how good I am with mediation between warring parties. I'm Equestria's premiere diplomat, after all. I know you'll scoff at this, but I want to know the details about your fight, so that I can better advise you in the future.
"Your Niece, Student, Friend,
Princess Mi Amore (Cadance) Cadenza."
* * *
Their next discussion was held, not over the cruel delays of parchment and ink, but face-to-face at tea. The pleasantries were exchanged, and the servants quietly dismissed, but even under her radiant smile, Cadence could tell the princess was gloomy.
"I got your letter, Cadence, and I thought it warranted an in-pony discussion." Celestia began, curtly, and the younger alicorn got the sense her mentor was irritated.
"What can you tell me about the fight that started all this?" Cadence asked, and Celestia's mouth became a firm line.
"Nothing, really. I noticed a few minor changes in Luna's behavior, she was more short-tempered and argumentative than usual. She went out of her way to anger the nobles."
Cadence nodded calmly, but inside, she was reeling. How did the sun princess not know her sister was changing? She didn't even know what the catalyst to her anger was.
"When I started to confront her about it (after all, the nobles were a huge monetary force back in those days) she just snapped at me and we argued."
"She just snapped at you? With no provocation?" Cadence repeated, forcing the dead-pan sarcasm out of her voice.
"One day, Luna simply refused to set the moon. It was a thousand years ago, but I still remember the gist of her arguments. A major point was that she felt under appreciated, for all the work she did, which was probably a fair argument. Secondly, she hated the fear with which our subjects treated her bat ponies, and others who appreciated her night. Lastly, she told me that I was an incompetent fool who gave in to the every whim of the nobles, and she no longer trusted me to run the nation."
"Ouch." The pink alicorn muttered quietly.
"'Ouch' indeed." Celestia sighed.
"About the incompetent part, was there anything you did, anything at all, that might have given Luna that impression?"
Celestia's eyebrow rose in silent question.
"Usually, these kind of complaints don't come from nowhere, Celestia."
"I know that, Cadence." Celestia sighed. "I just don't have any idea where it began. What did I do wrong? How do I fix things?"
"Well..." Cadence suggested, in the most calm and collected way possible. "You may want to approach her with humility."
"What?" Celestia asked, genuinely confused, and a little angry. "I am in the right of things! I am not the one who caused a war!"
"I know, Auntie, but sometimes you have a tendency not to admit your mistakes." Cadence sighed, as she sighed every time the topic arose. It was very difficult to argue with a sun goddess.
"The point is relevant. She started this, and I did not. We disagree on so many things, it would be hard to let that go." Celestia sighed dramatically, and slumped onto her desk. "I just want my sister back."
"What if she doesn't want to return home?" Cadance asked, and was met with a glare.
"Nonsense. Once the Nightmare is gone, she'll be sweet and loving again. You'll see."
Celestia was so certain, but Cadance wasn't that sure. It seemed like the sisters' problems ran much deeper than just possession or dark magic.
She hated to admit it, but Celestia might be too stubborn for her own good.