The deep, slow clip-clop of languid hoofbeats echoed in the still air of the Canterlot Castle library. Princess Celestia ambled slowly down the rows of books with a fluid grace that came from years of practice. Every so often her eyes would dart to a recently emptied spot on the vast array of shelves.

Twilight Sparkle, her former student, and now a princess in her own right, had asked very humbly for help in rebuilding Ponyville’s library. The tree itself was unfortunately destroyed beyond repair, and Celestia had made plans to consecrate the site and erect a memorial to the Golden Oak Library; one of the greatest works of earth pony hooves in all of Equestria.

Before that could be done, however, she had assisted Twilight and her friends in salvaging what little there was left inside the ruins, mainly only those items that Twilight had stored in the basement laboratory. She’d had to chuckle to herself when Twilight had turned her biggest and best puppy dog eyes on her and asked in her most timidly adorable voice if she could please spare some books from Canterlot to help rebuild the collection. Celestia had, of course, agreed at once.

Now, she let out a small sigh. She’d finished the selection of books to send, the couriers had carted them off, and the train was already on its way down the mountain. She had other matters to attend to, no doubt Luna would chastise her later if she left any of them over for the night watch, but something inexplicable was holding her back. A sense of trepidation and possibly nostalgia kept her roaming the rows of shelves in the silent room.

Celestia had just reached the doors and was about to leave and get on with the day’s work when a small sound caught her ear. She stopped; her ear perked and swivelled, followed by her head and soon the rest of her body. The sound was nothing more than a faint buzzing, and could have simply been an insect attempting to escape through a closed window. But Celestia knew in her heart exactly what that buzzing was.

Abandoning grace in favor of speed, she galloped to the shelf farthest from the door of the library, her hoofbeats producing sharp cracks that pinged around the vast room and rattled the books on the shelves. She skidded to a stop and lifted her eyes cautiously to the top shelf.

There in the center of the row was the source of the noise. Celestia shook slightly as her yellow magical aura timidly grasped the glowing, vibrating book and slowly brought it down to eye level. She felt a stitch in her chest as she stared at the symbol on the cover, a fiery red and gold sun, an image of intense power and passion.

Slowly, cautiously, she opened the book and flipped through the pages. Nearly all of them were blank, the writing on them having faded long ago to make way for new messages, messages that Celestia thought would never come again. Her heart pounded in her chest as she reached the midpoint of the book and felt the telltale spark of fresh magic on the next page.

Dear Princess Celestia,

For a long moment, all she could read were those three words, over and over again, ignoring the rest of the page. Even though written by hand instead of horn—Twilight had reported that the inhabitants of that realm had hands like those of a minotaur—the flowing script she remembered was unchanged.

Celestia’s breath began to come in slow, ragged gasps as the image of the page dissolved away behind a curtain of tears. Snapping the book shut, Celestia clutched it to her chest and sobbed for the first time in she dare not think how long. Utterly grateful to be alone in the library, tears poured from her eyes as memories of her former student flooded her thoughts.

When she first met her, the little yellow unicorn filly seemed so much like Celestia herself had been in her youth. She was driven, talented, immensely knowledgeable, and quite powerful for a filly so young. Celestia had been demonstrating the lowering of the sun for a group of students at her school when she noticed a blue-green glow emanating from the horn of a young blank-flank unicorn in the crowd.

As the sun began to dip below the horizon, the sky lit up with an amazingly colorful aurora. Bands of red and gold light covered the blue sky as it darkened toward the deep purple-black of twilight. The bright, luminous patterns framed the sun, dancing around and moving in sync with it as it disappeared from the sky.

Celestia very nearly fumbled the fiery orb, but concentrated on moving it slowly and steadily as she watched the flowing colors along with the rest of the students present, and indeed the rest of Equestria as well. She couldn’t help but notice that moving the sun this evening had taken a bit less effort than usual.

Celestia continued to watch as she finished her demonstration. The aurora slowly faded, lending a lingering light to the evening for a moment beyond the setting of the sun. Once the sky was dark, Celestia turned, and leaving the night sky blank and moonless for the moment, she beckoned the young filly forward. Her classmates shrunk back, unsure if they were about to witness a royal scolding.

“What is your name, my little pony?” Celestia asked in a calm, even tone, bending her long neck down to be not quite level with the filly, but not so intimidating as her full height usually was.

“Sunset Shimmer, Princess.” The young filly bent her front legs in a quick bow and looked back up, eyes firm and not a hint of trepidation. “I’m sorry if I offended you.”

“No, quite the opposite.” Princess Celestia smiled. It had been a number of long years since she had trained a student personally, and she couldn’t deny that it would be nice to have a companion to help fill the empty spot in her heart that had persisted for nearly a millenium. “I’m impressed; you have quite a lot of power for such a young unicorn.”

Sunset smiled and bowed again. “Thank you, Princess.”

Celestia placed a hoof on the filly’s shoulder as she rose. “If you’re willing, I would like you to become my own personal student. You show a lot of promise.”

Sunset’s eyes widened and she grinned broadly, not hesitating for a second. “I would be honored, Princess.”

Celestia smiled back and then blinked as a glow surrounded the filly’s flanks. She pointed a hoof at the red and gold sun that faded into being. “You seem to have gained more than just a mentor today.”

The little filly traced a hoof over her newly adorned flank and looked back smugly at her classmates, while Celestia turned again to finally raise the moon for the night.

At first, teaching Sunset was a great joy. She would plunge into each lesson eagerly, thrilled to be expanding her skills. She would often balk at reading assignments, but that was not unusual in a young student, and the frequency diminished as she found just how much there was to learn in Celestia’s selection of old tomes.

Sunset displayed considerable magical aptitude, often taking only a lesson or two to learn a new spell, and hardly longer thereafter to fine tune and master its casting. Celestia took great delight in her student’s prowess, charging ahead eagerly herself with more and more powerful spells than her lesson plan initially called for.

Unfortunately, despite her magical and academic scholarship, a disturbing symptom slowly began to arise. Although Celestia did everything she could to encourage her, Sunset was quite reluctant to engage with the other students at the school. The rare occasions when she did were brief, and often ended in arguments with her fellow pupils.

The records of her early enrollment at the school, which Celestia had initially forgotten about in her eagerness and haste, confirmed that Sunset had been somewhat of a lone wolf ever since her very first day. She was an only child and she had been singled out for a unique lesson plan—Celestia tried to justify the behavior initially, against her better sense of judgement, but the argument could not last.

Teaching her bright young student sadly grew to be ever more and more of a chore as the years wore on. Her casual dismissal of the other students at the school slowly morphed into outright contempt. Although she was careful to hide it most of the time, when Sunset became engrossed in learning a particularly difficult spell, she could become short and sometimes surly even with Princess Celestia herself.

Her earlier delusions almost completely cast aside, Celestia was nearly at her breaking point when Sunset made her abrupt departure. And even though there was a slight feeling of relief when she finally disappeared through the ancient mirror and the portal closed behind her, there was a much stronger feeling of regret and anguish left in Sunset’s wake.

Celestia always wondered if the fault lay with her for pushing her talented young student too hard in her earliest magic lessons, and for failing to instill the true importance of friendship with her fellow ponies.

Even harder to bear was the sadness and loneliness that came from losing a pony so dear to her. Fueled by the ever mounting tension between herself and Sunset, Celestia couldn’t help but recall memories of her sister, and how she had once lost the only pony she had cherished more through a similar failure to look beyond her own ambitions. She felt her lamentation more keenly as the thousand year anniversary of the loss of her sister drew ever closer, and her recent failure continued to prey upon her thoughts.

Celestia blinked back her tears and sniffed hard to clear her nose as she reopened the book and read the message within. She had been stricken when Twilight reported that Sunset had chosen to stay on the other side of the portal. But the knowledge that her former student was in the care of five people so similar to the ponies responsible for helping Twilight grow, and eventually even ascend, calmed the ache in her chest.

Her eyes darted over the words, taking in the plea for help. Celestia’s lips curled into a small smile as the realization hit her of the meaning this message held, far beyond merely that of the threat it mentioned.

That the self-centered loner, increasingly seeking solace in her own power and caring less and less for others, would now ask another for help was firm proof of Sunset Shimmer’s rehabilitation. Celestia clutched the book back to her chest, breathing deeply. She wept once again, but her tears were now tears of joy, peace, and contentment.

“Sister, are you alright? You were not present at breakfast and I feared you would miss your appointment with the Diamond Dog ambassador. He is eager to speak to you regarding Twilight Sparkle’s new realm and the effect on the borders of their land beyond the Everfree.”

Luna’s voice broke through her reverie. “Sister! Yes, I am fine. I simply have an unexpected situation that must be attended to promptly.” Celestia’s hoof stroked the cover of the book as her horn glowed briefly, feeling out the position of the sun in the sky. “I don’t suppose you could stall them for, say one half hour?”

“Leave it to me, but do please hurry. I needn't remind you that they are already notably upset after having lost some of their northern territory with the return of the Crystal Empire. Princess Cadance and Shining Armor have reported even more disquiet on their borders of late.”

“I will act with all haste. Thank you, Luna.”

Luna nodded and strode away.

Celestia flipped open the book and touched her glowing horn to the page with Sunset’s message, marking it unread again. The book began to glow and vibrate once more as she took off and slammed through the nearest window, banging the shutters open as she dove toward the edge of the mountain below the castle.

Celestia regretted that her long reminiscence now left no time to write a reply herself. According to her message, Sunset needed help fast. With the portal closed for many more moons to come, Twilight would have to engineer some kind of solution out of the mess of parts they’d salvaged from her lab. The fact that the book functioned between worlds made it a vital link that Twilight would need.

As much as she desired to, with the Diamond Dog summit looming, Celestia could not afford to remain in Ponyville. Still high in the air, she could see the train just reaching the base of the mountain and beginning to steam along the plain. With luck and a good tailwind she could arrive just as it did and drop the book on top of the lead cart, where it would be easily visible. The message inside would be enough for Twilight to take the necessary action. She pumped her wings and pushed against the air with all her might.

“Help is on the way, my beloved student.”

Author's Notes:

I got the idea for this scene because if there was one disappointment I had with Rainbow Rocks, it was the complete lack of Princess Celestia getting to hear from her former student after she seemed so concerned about Sunset Shimmer during Equestria Girls. Especially keeping the mirror by her side in case Sunset ever came back.

The movie made it seem as if the book just happened to be part of the pile that got shipped to the Friendship Kingdom Palace, showing up at just the perfect time. Instead, I envisioned a scenario in which Celestia placed the book in Twilight's possession when it was needed. The rest of this bittersweet tale naturally fell out of that premise.

Also: Not precisely fan art, but SkycatcherEquestria over on deviantArt found this story while in the process of drawing a little scene that could very well fit right in the continuity here. As far as I'm concerned, it's canon.