At the edge of Equestria, a cave sat at the bottom of a cliff.
The cave yawned open, a black gash into the craggy cliff-face. Vines framed it, clutching at the rock on either side. It was a quiet, verdant place at the utmost edge of the Everfree. Here, a pony could forget themselves, put away their worries, forsake Equestria for the sound of the wind whispering through tree branches. It was rare that a pony would find it, though. It wasn't a place that was advertised.
Celestia stared, unblinking, at the cave entrance. It rose before her, silent and still and extending into darkness.
"Princess Celestia?" came the voice of Captain Eyewall from behind her. "Shall I escort you inside?"
She glanced briefly to the pegasus captain, whose bearing betrayed nothing past his customary grimness. He stood by the chariot that had delivered them in an hour's hard flight from Canterlot, several other members of her own guard by his side. Their golden armour caught the rays from the midday sun, from where it hung still in the sky.
Let it hang there. She could afford to keep it still for a little while. She would need her attention elsewhere.
"No, captain. Have the Dayguard keep a simple perimeter watch. Should you need to find me for any reason, the guardian will recognise your insignia and let you through." Celestia noted her brusqueness of tone only too late, and hastily corrected herself. The Sun Princess should not be flustered or abrupt when nopony else had reason to expect her to be. The princess serving Equestria would be the creator of harmony, not the destroyer of it. That was the protocol, as yet iron-hard as the first day she'd resolved to it.
Amazing, how time and all the memories it could hold had a habit of rusting iron clean away. She gathered herself regardless, an effort that was all but reflexive.
Don't let them see your fury, whispered a little voice within her, like the crackle of flames in a hearth. Save it for him.
"Yes, Princess," said Eyewall. The captain's restlessness betrayed itself in only a brief glance towards the cave, a momentary hoof-scuff across the ground. The stallion was a professional. "Should we … expect to engage in any sort of rescue efforts?"
"No, captain," replied Celestia, turning her gaze from the cave's blackness and to her doughty soldiers with a brief flash of relief. "I know this place. I inherited it in past days, laid its present enchantments and foundations. No part of it is unknown to me. Remain on guard for threats from without, regardless. Better safe than sorry, wouldn't you agree?"
The captain hesitated for a moment before answering. "Yes, Princess. Are you sure you don't wish for an escort?"
"I'm sure, captain. There are reasons – several very good reasons – why I must do this alone." Celestia stepped slowly towards the entrance, breaking several minutes of rigid stillness at long last. "I may be a while. Do not grow alarmed."
She heard Eyewall's affirmative, heard the movements of her guards as they shifted into position. They had been a formality for her exit from Canterlot, for what her government had been assured was a brief visit by the princess to the Cheval Sea's Serpent King to formally appraise a close ally of recent events. The Serpent King had been long since appraised via letter, though, and Eyewall and his guards had been sworn to secrecy about their true destination.
Celestia stepped past the cave's entrance. The cold and stale air hit her like a hoof to the face, and a flurry of golden light around her horn conjured something she could navigate the dark and twisting passages within by.
She passed by an unheeded metal plaque set into the wall, the only acknowledgement this place would ever receive beyond her own knowledge and that of a few trusted others.
Herein lies Tartarus, read the lettering upon it. Entry to this guarded location is forbidden by order of Princess Celestia. Turn back on pain of death.
Celestia stepped into the vast cavern past the first few hundred winding steps from the entrance, and the guardian of the place was upon her in seconds.
"Get off, you affectionate lump," she said, a laugh escaping her despite the occasion as all three of Cerberus's heads attempted to cover her in slaver at once. "This isn't even slightly becoming, and I suspect you know that and don't care."
The three-headed, house-sized mastiff appeared not to give not the slightest damn about her blandishments, two heads continuing to sniff and lick her while the third barked with abundant joy. The sound echoed off the distant roof and walls.
"Luna's back, you know," said Celestia, letting emotion slip into her voice as she spoke. The joy of it was yet near, the occasion only yesterday, and the high of it ran still. It had been a chore to tear herself away from her sister and come here. She blinked away sudden inconvenient rainwater from above, and nuzzled one of the great dog's necks. "She'll be over here to spoil you and make a fuss as often as she can spare the time. Just you wait."
Either Cerberus recognised 'Luna' after all this time, or it had gotten the phonemes for 'dinner' jumbled up in its heads, or it had just started spontaneously happily baying for no particular reason. It was hard to tell.
It remained, as it had always done, the first and last defence of Tartarus. The first against unwitting intruders from outside, whom it would greet with a great deal of intimidating snarling and barking and minimal clouts with a door-sized paw. The last against any of Tartarus's potential escapees, whom it would deal with in a much less restrained manner.
"Here on business myself, though," murmured Celestia, pulling her face away from the dog's neck and briefly wiping her eyes dry, regaining her composure in spite of Cerberus's best efforts to destroy it. "Get off, I said. I'll play with you in a few minutes."
Cerberus's perennial deafness to instructions eventually compelled her to become airborne, just out of reach of Cerberus's pouncing. It bounded after her, three heads turning to track her, and set up a sorrowful three-way yipping as she flew past the furthest length the thick steel chain tethering Cerberus to the cavern's centre would allow.
"Please don't. Don't make me feel guilty now," sighed Celestia as she alighted at the chamber's far end, before another seemingly-insignificant tunnel leading further on. "Really, don't."
The runes carved around the floor, walls, and ceiling of the tunnel briefly flared a luminous blue as she stepped nearer. If Celestia passed through correctly, then she would gain access to the rest of Tartarus. If she missed a step, whether coming or going, then a battery of the worst warding-magics known to Equestria's magical science would flay her apart down to her atomic structure in one excruciating half-second.
Lucky then, all things considered, that she knew the magical key to be formed in her mind that would let her through. It had been Scorpan who'd taught her the way of it and granted her the place's wardenship, back in days where even her memory was starting to develop fuzz around the edges, and he'd apparently inherited it from Star Swirl himself. When and who it had all started with, Celestia had no idea. When and who it would end with, she didn't want to know.
She composed the key, accurate down to the smallest detail, and passed through the ward. And the one after that, And the four more after that.
Dark stone doors passed her by as she trotted, each one leading either to another stretch of secured corridor or to one of Tartarus's many inhabitants. More warding runes and enchanted carvings covered each one, bathing the tunnels in a soft blue light. On one, a central carving of what looked like a looming black tidal wave predominated. On another, what looked to be a constantly-spinning spiral with an eye at the centre. On another, a flame. On another, an empty circle.
Celestia turned left at one juncture, passing through the door to another corridor. A dripping thorn. A horned pony. A staring shadow in a door frame.
She turned right once more, and at the end of the short corridor ahead of her, there was a door with one more carving. A horn, wings sprouting from either side. It was the only one of its kind in this section of Tartarus.
Stepping slowly towards it, she cursed herself for her own hesitation. She was Princess Celestia, eternal and ever-sovereign. She would do what was best for her little ponies, she would do what was right, and though she saw most ends and knew with a sad and grim certainty the end that would come of this, that didn't take away her duty to see it done. She had to have hope.
Celestia unlocked and pulled open the door, stepped through into the blackness beyond, and closed it behind her.
Let there be light, she willed, and there was light. It was as bright and golden as a summer's day, radiating down from the low stone ceiling.
On the floor before her, a chained alicorn stirred.
It was a stallion, with a coat as black as the night sky. Bright silver spots were dappled lightly across his whole body, clustering more thickly around his head and back. His mane and tail were predominantly white, with luminous strands across a spectrum of colours woven throughout; red and orange, yellow and silvery blue. A mark of a gold-and silver star glinted on his flank, eight points protruding from it.
Iron chains thicker than his muscled forelimbs were wrapped around his legs and body, pinning his wings firmly against his side. A magical inhibitor with all the squat chunkiness and aesthetic appeal of a block of coal was jammed down around his horn, all the way to the base. Barely-glimpsed magical energies flowed around his head, informing the deep sleep he appeared to be in. The energies had thinned away since the moment Celestia opened the door, however, and the alicorn's body began to stir.
One eye flicked open, and a black-rimmed pupil of purest white stared straight at Celestia. The other slid open in time, and the expression on his face remained emotionless and cold.
Celestia spoke first. "Astralus," she said.
Astralus took several moments to respond, and when he spoke, it came out as a low rasp. "Celestia."
The Star Prince slowly started to rise to his feet, straining against the sheer weight of chains enveloping him. He looked directly to her once he had fully risen, his eye level an inch below Celestia's own. His expression contorted into a sneer. "So," he began, "How long has it been this time, dearest sister? A year? Two years? A decade?"
"One hundred and ninety years have passed since last we spoke."
An instant passed before Astralus's white pupils widened and his nostrils flared.
"ONE HUNDRED AND NINETY YEARS?"
"Yes. You needn't shout."
"And what could have possibly caused that delay?! Sheer stupidity? Pausing in your princessly duties to pursue a butterfly for two centuries? Did you forget where Tartarus was?"
"I refer you to my earlier comment regarding the need for shouting."
"You useless, maggot-riddled, empty-skulled BROOD-MARE!"
Celestia remained silent while the invective broke over her like water on a rock. Astralus frothed and raged within his chains. Let him.
"Would you believe that the affairs of Equestria kept me absent for that time, in spite of the pleasures offered by your company?" she eventually said acidly. "Many things have happened in Equestria since we last spoke. New bearers for the Elements have been found. The Crystal Empire's heir has re-awoken. Luna's imprisonment has ended, and she has returned to Equestria."
Astralus's voice fell away, and his gaze flicked from the floor to Celestia. "Well," he said, his tone low and venomous once more, "That makes sense. That makes perfect sense, all things considered."
"Does it?"
"Small wonder you'd wait so long, for fear of risking facing me once again by yourself. Better to wait for more alicorns, that they might be able to restrain me. Small wonder a weakling like you would wait."
"Weakling?" Celestia tried to curb the contempt for the alicorn before here, so pathetic that he was almost funny. "An odd accusation, considering I was the one who put you here."
"Aye. To keep me and the power I hold safely locked away! To prevent my disruptions to your fawning, cowardly plan."
"Luna is released at long last," repeated Celestia, driving past what promised to be another interminable period of raving. "I am prepared to offer you the same. To give you a chance to walk free in the world once more, to start rebuilding that which you tore down. There will be conditions, until Luna and I both can be assured of your future good conduct. The continued restraint of your magic, to a level not exceeding that of a competent unicorn. The binding of your wings. Your domain will not be immediately returned to you - "
"Hobble me, cripple me, keep the stars from me. What lovely terms."
"There is an alternative," said Celestia, past teeth that itched to be ground together, "Consent to a magically-binding geas, compelling you to not rebel, to harm nopony ever again. You will have your alicorn magic, your wings, your stars back again. But the penalty for violation would be inescapable, and would - "
"Hobble my free will. My word, this bargain escalates in desirability with every beat of my heart." Astralus's eyes narrowed, becoming mere monochrome slits. "Here is my offer. Release me as I am. Trust me to do what is best. Do not get in the way of that."
"You really do take me for an idiot." This time, Celestia ground her teeth, trying to ignore the nagging voice in the back of her skull that ordered her to forget every memory, abandon all hope for him, to simply burn this waste of oxygen and space off the face of Tartarus with all the fury the sun would grant her. "I remember the last time you walked unfettered."
"Oh, spare me your sanctimonious bleating about Seaddle. As if a few worthless mouths ever mattered."
"Nine thousand, three hundred, and forty-seven ponies," said Celestia quietly. Far too quietly. Far too restrainedly. "Two thousand and eight foals. I counted afterwards, once the smoke cleared and you were locked away here. I remember."
"Oh, I see. Still pretending that you care. Still blind to your own weakness. Craving the approval of your lovely little ponies, are we? Fretting over every impolite thought they might have against you, whimpering yourself to sleep over the prospect that they might not think you have their best interests at heart? Why do you bother? What a supremely pointless ploy."
"What a supremely revealing statement from you," said Celestia. Her voice was still as quiet as the eye of a storm, but a wearied undercurrent had set in. She had nobody to blame but herself for this pointless pain. She saw it coming before it ever occurred.
"We are GODS on this earth!" screamed Astralus, his eyes blazing white and his wings straining against his chains to be outspread. "We made ourselves gods, we clawed those teachings from Star Swirl's notes, we unravelled them, we made ourselves free! We should have anointed ourselves kings! Emperors! Not meek little princes and princesses, mincing around in the mud for the sake of meaningless little ponies. All they are, all they'll ever be, are spectators. Chattel. Tools in our grasp."
Magic comes alive in this world when an alicorn is born from the shell of a pony, Star Swirl's notes had read. It warps and weaves, and in its vast caprice it flips a coin for the alicorn in question. On one side, the alicorn is born intact. On the other, the alicorn is broken.
Once upon a time, Celestia recalled, there had been a white-coated earth pony filly who had pored over those same notes. And thanks be to whatever greater powers ruled in this world, she seemed to have come out intact. For the love of Equestria, let her remain so.
There had been a pegasus filly, indigo-coated and alive with life, who had come out of that coin flip cracked but still whole. Who had once surrendered herself to the Nightmare madness that haunted every alicorn, but who would heal in time. Celestia would permit no other outcome.
And there had been a black-coated and gentle unicorn colt as well. He had gone through that coin flip, and had come out the other side with a Nightmare made redundant by the ruins of his mind.
You couldn't heal that. You couldn't banish a Nightmare that had never been needed at all.
For that colt, Celestia felt an aching sorrow, and a pity that could never be soothed. But all it could do here was give fangs to her hatred for the beast before her.
"Luna was banished by the Elements, the Crystal Empire fell from our holdings, and you seemed set on your foalish course. I returned from the wilderness, gathered my host, and tried to remind you of the proper path. A gentle reminder and nothing more, and you cringed away from the promise of your own strength. You locked away your own brother, a bond forged in fire and Discord's ruin, just to appease the nonentities you serve. Pathetic."
The fire rose in Celestia.
Let him burn, it whispered. Nopony will see. Nopony will ever know. Luna will understand all too well. Burn him and leave his ashes to the darkness. Burn away the memories of the foals lying in pieces, and give them true justice.
Burn him, burn him, burn him, whispered the Nightmare at her hooves.
She tensed, every part of her horn itching with magic that begged to be released.
And then the image of the Sun Princess came like a wave to wash it away. Watching her sister adorned with a wreath by foals, watching Twilight Sparkle's boundless excitement at being chosen as Celestia's personal protege, watching a hundred generations of ponies live and die and love and remain safe and happy under her guidance – the Nightmare shrank back.
But not entirely.
Give me something, it whispered. Or there will be fire in your dreams.
Celestia breathed out, and her voice remained collected and steady.
"I see this was wasted effort," she said to no-pony in particular, Astralus's gaze flicking to her with a newfound intensity. "Maybe it always will be."
"You came here with a purpose," came his response. "Show some spine for the first time in your waste of a life and see it through. Try and put shackles on me. See how your ponies will whisper in corners. How they'll shrink from the monster returned from legend."
"I doubt they will," said Celestia. "I did what I had to to patch over the wounds." She leaned closer to Astralus, her magenta eyes glinting like cut diamonds. "They don't even remember you existed at all. May they remain happy and ignorant forever."
"You can't just leave me," rasped Astralus, a new edge in his tone.
"Can't I? I have that in my power at least," replied Celestia, turning away and stepping towards the door. "Goodbye, brother." She stepped through the doorway. Magic built around her horn to seal the enchantments once more. And her Nightmare got this much, for all that she wept at herself and it, for it was all that would keep her sane. All that would keep her the good princess against the demon in her heart.
The sleeping enchantment wasn't cast.
"No," said Astralus, and then, "No!" again at her back. "You came here to offer me freedom, so let me go! I'll take the shackles! Come back, Celestia! Celestia! Sister, don't leave me again, you offered me freedom, I'll take it, I'll take the shackles, don't leave me, PLEASE - !"
The door slammed shut.
