Never before had the atmosphere in Canterlot Castle felt so heavy, so oppressive.

The marble seemed to lose its luster, fading to a matte, joyless white, and even the stained glass windows with all their beautiful depictions of Equestria’s greatest heroes had bled away to a dull gray.

Twilight sat at the dining room table across from Princess Celestia, her eyes flitting to the empty seat and plate on her right side. She chewed on her lip, her ear twitching at every sound as though she expected Luna to appear suddenly in a cloud of mist and stars to wrap her in a powerful feathery embrace, nuzzle her ear, and whisper honeyed words that would make her cheeks burn and her heart flutter.

Sadly, it was not to be. She knew it wouldn’t, of course. Luna had only just fallen asleep an hour or two ago at most.

A small mercy, really. Hopefully, her nightmare won’t return. She needs her rest.

“You’ve barely touched your food,” Princess Celestia noted, her voice only just above a whisper. “Or your tea.”

Twilight didn’t even spare her plate a glance as she nudged it away with the back of her hoof. “I don’t have much of an appetite this morning.”

Her teacher sighed and rustled her wings. “Neither do I. Not after last night. It’s been …” she trailed off, her ears drooped low. “Far longer than I can remember since I last saw her so distraught over a dream. Not since we were fillies, I believe … her own, that is. The things she’s seen in nightmares …”

A pang shot through Twilight’s chest. The visage of Luna’s tearstained face, her teal eyes wide with horror as she desperately held Twilight against her for comfort, not to leave flashed rose to the forefront of her mind.

No, she thought. Luna wasn’t holding me for support. Not at first.

Luna had been trying to keep her from seeing something. Or, rather, somepony.

That alone was enough to make her wonder. Just who could inspire such fear in the Princess of the Night? Within her own realm, no less! And what could make her so desperate to beg that they—especially Twilight—not leave her side, even for an instant.

Twilight took a sip of her lukewarm tea. “I wish I could help her,” she said. “What in Equestria could be bothering her so much?”

Princess Celestia didn’t reply for a moment. She drew in a deep breath through her nose and took a slow sip of tea. Her eyes closed. “Perhaps I should’ve refused when she offered all those years ago,” she muttered. “Maybe then we could have ruled together these past thousand years.”

Perking her ears, Twilight tilted her head. “I’m sorry?”

The Sun Princess shook her head and opened her eyes, but didn’t look up. “Apologies. My mind wandered back to some rather … in hindsight, some mistakes that I wish I could go back and change more than any others. And more so with each passing day.”

Another vague answer about Luna’s past—her Luna.

No. She wasn’t having it this time. Not after last night.

Twilight set her cup down on the saucer and laid her hooves on the table, folded neatly one atop the other. “Princess,” she began, “I truly hope you’ll forgive me for being so bold as to pry into family affairs, especially ones so close to heart, but after last night, I feel I have the right to ask what has my girlfriend so upset.”

Her teacher’s brows raised a fraction. Barely more than a millimeter. On anypony else, they may as well have disappeared beneath her flowing mane.

Which left Twilight only a little room to press the advantage. “I want to understand how she went from beloved and influential to lonely and isolated,” she continued. “I want to understand what drove her to become Nightmare Moon so I can help her move on past whatever it is that makes her look so regretful and caused such a horrible nightmare. I want to know what’s making her own domain turn against her so I can help my girlfriend. Please.” Twilight leaned forward. “No more skirting around the question or telling me to look for things. No more leading me around. Help me help Luna.”

Pristine white ears twitched. The final word seemed to reverberate through the dining hall, loud enough that all the Day Guards posted within, and even the pair posted just outside the door, could hear her plea as plain as day.

Then Princess Celestia closed her eyes once more and smiled. “You’re right, of course, my brilliant student. Luna’s heart is yours, and her well-being of equal concern to my own.” She let out a deep, shaky sigh. “You must understand my dear, I am not proud. All that you wish to know is as much my fault for my blindness and neglect as she claimed as hers when we began down the path which led us all here. There is no greater shame in my life, no choice I wish I could take back so earnestly. This, Twilight Sparkle, was, and ever will be, my greatest failure.”

Regret. Shame. Both so raw and painful, as if events from centuries long passed had happened a few short years prior.

Family drama far older than the blood feud between the Hooffield and McColts.

But why?

“You must swear one thing to me,” Princess Celestia continued.

Twilight blinked. “Anything.”

“Nothing I tell you will ever be discussed with ponies outside of this family. Unless Luna deems it permissible.” Her feathers twitched. “The past has haunted her enough. I don’t want this to rear its head as it did in those days and ruin what little she has left.”

Twilight reached across the table and laid her hoof upon Princess Celestia’s, just as the latter had done for her so many times. “I just want to help Luna. I promise I won’t tell anypony, I swear on every spell you’ve ever taught me and all the late nights we studied together that it won’t change how I view either of you.”

Slowly, Princess Celestia opened her eyes. Her calm, stately mask could do little to hide the pain flashing naked across her face.

“Don’t be so sure,” the Sun Princess muttered. “If you truly wish to understand and help her, there’s only one thing for it.” She rose from her seat and beckoned Twilight to follow. “Come. It’s been some time since our last history lesson. We’ll need to take a little walk to find our materials.”

Twilight rose as asked and hurried to her side. “Where are we going?”

Silence fell between them for several seconds.

Another sigh came forth as Princess Celestia bowed her head. “To the place where I hid my pain.”

Twilight had expected a long walk down a secret flight of stairs, down into the very depths of Canterlot Castle’s forgotten dungeons from days long forgotten, when the land was wild and untamed. Or maybe for a sky chariot to be summoned that would take them to the very summit of Mount Canterhorn to visit a fortress or cave with a big steel door and a series of locking spells that responded only to Princess Celestia herself, and no shortage of unpleasant surprises to any other who dared attempt to tamper with it.

Indeed, they did take the long walk through the castle’s corridors, tracing a path she was quite familiar with. Day Guards saluted at their posts, sunlight bathing the castle in its glow as they turned to trot down the lone staircase leading to some of Equestria’s most guarded and hallowed source of knowledge.

The Royal Archives.

The Day Guard posted saluted with his spear as he saw his Princess trotting toward him, then moved to push open the door to admit them. Princess Celestia nodded and thanked him as they passed, never breaking stride as she continued on toward the desk at the far end of the Archives.

Page Turner rose from her desk without prompting and bowed low. “Princess,” she greeted. “Twilight. How may I assist you today?”

“We’re going to visit the last room, Page, for a little history lesson.” As the Princess spoke, Twilight noticed the old librarian’s eyes widen and the color drain from her coat. “Yes, that one. I’m going to need you to bring me a couple books for supplemental material as well.”

“O-Of course, Your Highness.” Page Turner bowed once more. “Whatever you need.”

“Just Werner’s journal and that … charming summation of the Night Guard’s history. I’ll await your arrival in the first entrance before locking the door, but do be quick. Twilight and I have some rather urgent matters to attend to, and this information is critical.”

With a squeak, Page Turner scuttled off toward the lower security rooms to retrieve the books.

Princess Celestia didn’t wait longer than a second or two before turning to trot in the opposite direction. “Come along, Twilight,” she called with a flick of her wing. “We have quite a bit to cover, and I suspect Luna won’t be asleep for long. She’ll want one of us there when she wakes.”

Hurrying to her side once more, Twilight cast a quick look back in the direction Page Turner had gone. “Is it really so necessary to lock the door behind us when we’re already inside?”

Her teacher shook her head. “We won’t be, not when Page brings the books I requested. This room we’re going to is … special, I suppose is the best word.”

“Special how?”

“Special in that the door you might see if you were to pass it by while looking for a book is merely the door I had put in place to keep ponies from happening upon the actual door.”

Before Twilight could properly wrap her head around the notion, they came to a door in the far corner of the Archives. She took a quick glance at the top of the doorjamb, curious as to what symbol might hint at the contents, but found none.

Instead, there was a single sign nailed to the door which read simply: “Do Not Attempt Entry. Violators Will Be Prosecuted to the Fullest Extent of the Law. By Order of HRH, Princess Celestia.”

“Heavy secrets then,” Twilight said.

“More than you know.” Princess Celestia inserted her horn into the keyhole and twisted counterclockwise. The latch clicked open with a dull rattle. She withdrew her horn and pushed the door open with a casual flick of magic, then gestured for Twilight to enter. “After you.”

Curious, Twilight entered with the slightest hint of scholarly glee flickering in her chest, even through her worry for Luna’s sake. What could there be for her to learn? What hints from the past could bring Luna out of the darkness she’d hidden away in since her return and forgive herself?

She expected a similar scene to the last room she’d visited. A room lined with bookshelves packed to the brim with texts so old and valuable that every bank in the nation could empty their coffers and still come up far short of ever purchasing one, and then a lone work desk where one could read and take notes at their leisure.

There was nothing but empty space. Before her was a room with white walls and tile, barren of any decoration or hint that anypony might be permitted to sit, save for one thing on the opposite wall. The second door.

A golden shoed hoof touched her shoulder. “Don’t try to open that door,” Princess Celestia said softly. “Only Luna and I are keyed to the wards I laid when I created this place. Any other who tries would find the consequences most unpleasant.”

Twilight couldn’t help but ask, “Unpleasant how?”

Her teacher paused in thought. “When I created the wards, it was rather shortly after Luna’s banishment. As you might expect, I wasn’t in the best state of mind, so I slipped into some old habits.”

“… Meaning?”

“Meaning that I was not always kind and merciful to those who came seeking to harm my ponies. And in matters concerning Luna’s belongings and very heart while I awaited her return—” something flashed in her eyes. Fury. Raw and untamed, like a raging inferno. “—I found that overkill was nowhere near enough.”

Almost as soon as the words left her mouth, Page Turner scuttled into the room with a pair of books held aloft in her magic. She passed them over to Princess Celestia with a quick mutter and bow before hurrying from their presence, though not without closing the door behind them.

Princess Celestia didn’t wait but a second before her horn flashed a brilliant gold. Her magic engulfed the series of latches and locks riddling the door and flicked them shut one by one. Then she turned toward the second door, her feathers twitching anxiously as she approached. A tendril of shimmering gold reached out, washing over the door.

Twilight could feel a static tickle run down her spine. Her breath caught in the back of her throat. She stood several steps away from the door, yet she could still feel the wards disengaging in response to her teacher’s magic. Whatever Princess Celestia was protecting for Luna, she placed far more worth upon it than priceless texts and journals she kept locked away in the other rooms.

The door opened with a slight creaking of hinges to reveal a stone wall and staircase which spiraled down into the depths of the mountain. Princess Celestia’s horn flashed again, which coaxed a flickering orange glow from somewhere along the path. Torchlight.

There was that secret place Twilight had expected.

Without a word, Princess Celestia began to descend the stairs, with Twilight close behind. Down, down they went into the depths of the secret tunnel cut into the very heart of Mount Canterhorn. Idly, Twilight glanced at the walls to take note of the smooth surface, as if the stones had been cut and polished not by chisel and hammer, but by intense heat.

Fire magic, she concluded. Fire magic whose wielder was unmatched in power and precision.

And the foremost wielder in history was leading her deep into the tunnel she dug a thousand years ago. All to protect her sister’s belongings and hide her pain.

At long last, they came to another door. Again, Princess Celestia had to disengage a series of wards before opening it, and once again Twilight felt her coat bristle with each release of magic.

Before pushing it open with her hoof rather than magic, Princess Celestia paused and glanced over her shoulder. “Do you remember the night Luna brought her old records?” she murmured.

Twilight bobbed her head. “I said they must have been preserved with a powerful spell.”

“The most powerful one I know,” Princess Celestia confessed with a tiny smile. “I would not allow her to return to the world without the things she held dear, even if I could not fashion friends for her. Nor could I bear to look at them each day and remember how much I failed my responsibilities to her.” For the first time in all the years Twilight had known her, she saw tears gather at the corners of the Sun Princess’s eyes. A shaky breath forced its way from her mouth. “In a way, I suppose you could say my efforts to govern justly these past thousand years have all been my penance. But every so often, I would come down here and remind myself of how beautiful and lovely she had been before.”

She pushed the door open to reveal not a room, but a full art gallery.

Twilight’s eyes went wide, her jaw dropped.

Over a hundred paintings lined the walls, more vibrant and detailed than even Cadence could ever hope to match. There were scenes of the night sky, of young ponies at play, Princess Celestia radiating sunlight as she extended her wings toward ponies in need, and musicians pouring their very soul into their instruments to coax forth beautiful music. Then there were the sculptures. Oh, Twilight knew each of those figures, but none more than the largest and most splendorous situated at the far wall in the most prominent position. She knew their names. Everypony did.

Clover the Clever.

Princess Platinum.

Private Pansy.

Commander Hurricane.

Smart Cookie.

Chancellor Puddinghead.

The Founders Six, all seated at a table together with broad smiles, their assorted headwear removed and placed upon the table. They weren’t meeting as leaders of rival tribes, or even leaders of a budding nation.

They were dining together as friends.

Twilight stepped into the room, her eyes darting this way and that to try to take it all in at once. She felt the magic tingling in the air, ever-present in its duty to preserve all of the wondrous works until the day their creator deemed the time right to share them with the populace once more. “This is … all of this …”

“Yes. There are several rooms if you wish to see them as well.” Princess Celestia closed the door behind them, then moved to lay a wing across her student’s shoulders. “This is where I kept my sister alive for all those years.”

Then, she took a shaking breath and added, “This is where I come to remember the night before I took the light from her stars.”