It could have been night. It might have been day. Ultimately, it did not matter.
There was barely enough light in the dungeon room to make out the roughest outlines of the occupants, at least for one of the siblings. The younger could see perfectly in the dark, had been able to since the moment her after had begun, and the older could light things up with a thought. But they rested their bodies against the floor, assuming postures of physical calm which were in no way reflected by either mind, and neither did anything to change the lumen level. For one was most comfortable in the dark, and the other simply did not wish to look at anything in the real world, for the images playing within the internal theater had taken so much of her attention.
They had chosen the dungeon for privacy. For a complete lack of those who would take the too-calm words and spread them into the rest of the realm, creating a panic nopony would be able to stop. And because it felt appropriate somehow, that the prisons their bodies might become were momentarily confined within an inadequate secondary one.
Sometimes the room was hot. At others, it was cold. Neither occupant noticed.
In soft tones, with the burden pressing down on each and every syllable, they wrapped up the inevitable conclusion of what had become the best-case scenario before finally beginning to make their way towards the true last resort.
"We're sure she's their daughter?" Celestia asked. The words were not weary. The words had deliberately not slept in more than a thousand years, for every moment of rest would have produced nightmare.
Luna sighed. "I have viewed both their application and the records from the hospital. I suppose there is always a chance that Rapture could have gone through a brief affair which coincided exactly with the time of the application: I am uncertain as to whether --"
Celestia shook her head. "One thing about that spell -- it doesn't work on a mare who's already pregnant. The medical caster would know something was wrong. And if they'd come in for the birthing without the paperwork, then the doctors would have had to track down the pony who performed the working without the application having been filed..."
Luna's head dipped. The stars in her mane were dim, and the borders had not shifted since they'd entered the room. Neither mane was moving at all. "Then there can be no doubt. She is of their blood."
"Yes."
Technically, the working was known as Mytilene's Truest Love, but virtually everypony simply called it The Most Special Spell. It did one thing only, and it did it perfectly. Any two mares under its effect could have their own foal -- one which would truly be of their blood.
There were some flaws, or at least technicalities. The spell only worked on mares to begin with, for the biology necessary to carry the unborn still had to be present. (Attempts to create something for stallion pairings -- a working where the resulting offspring could be brought to term by a helpful mare --- had been numerous, and all had failed.) Any pregnancy which resulted from the spell would be normal, but those pregnancies didn't always happen: unless cast by the strongest, the working lasted only a single night, one where there was the same chance of a mare at the peak of her cycle becoming gravid as there was for any other method, and it meant repeated castings were often necessary. The resulting foal would always be a filly: anypony wishing a colt in the family would generally have to adopt -- and Celestia had watched slow centuries pass as the mare population within the realm gradually increased while wondering about the true cause of the tilt.
Unscrupulous unicorns had tried charging desperate pairings thousands of bits per casting. Some of those had no ability to actually perform the working: they collected bits, created glow, and fled. Others stayed just long enough to watch the conception attempt. Celestia had rapidly become fed up with all of it and made castings free, available from the government to married couples (or rarely, on up) after filling out a simple application -- but that application had to be filed.
She had been a little worried about the spell when Mytilene had first announced it, and that concern had been centered around disease. (The opinions of those who screamed about violations of nature had mostly faded out after the first hundred years.) There were problems of the blood which occurred only on the mare side of the population. If a mare who had those issues paired with a stallion, their fillies seemed to have a lessened chance of manifesting the same disease. Mare with mare... she had been worried about two sufferers finding each other and giving their offspring a seeming guarantee of blood-borne illness. As such, there was a health screening involved prior to casting, as much as magic and science would allow. Minimizing the risks.
If Joyous' state was truly from something in the blood, then the Releases had slipped through a crack nopony had known existed.
"Some diseases of the blood can be moderated," Celestia said. "There are treatments for a few which allow their bearers to lead normal lives -- they're just treatments which have to go on for a lifetime, Luna. Cures... nothing's been found which would be permanent. But if it's in the blood... there's still hope for her. Now that we have her parents here, there's even more ponies to inspect, conduct tests on... if anything, her odds have gone up a little. I could say the same thing about -- the other option, but..."
The younger's eyes were closed now. "Yes. We will reach that. But let us conclude with this portion first. Should it be in the blood, there is a chance still... but not a strong one. We could look for others who suffer from it, but... that also comes into the next part of our discussion."
Celestia slowly nodded. "What do you think about the ways it's manifesting? They all clearly have the same thing, but... from what you said, it's affecting their minds, and Joyous is rational..."
"I am guessing," Luna quietly admitted. "We are dealing with a condition never before seen, at least in this manner, along with a mark paired with a talent which nopony had previously manifested at all. But it seems to me that if the condition forces the intensification of magic... then at least in the sense of any deliberate actions taken by the mark's possessor, Joyous' talent is passive. She does not try to exude sex appeal. She does nothing to make herself more arousing. She simply is. The magic -- for whatever magic might be happening at all, which we cannot find on ourselves -- is thus free to go on at all times, regardless of her actual activity. With her parents... weather surveying is an action. Something which must be actively pursued. In order for the increased magic to find expression, those with the condition would need to be performing those actions. And so they are twisted from within, caring less and less about anything outside the range of their talent, doing nothing else unless it keeps them alive for the next display. They eat for fuel, they sleep for rest, they travel and arrange jobs because that is a minor part of their mark, at least for now... I suspect they would be offering services for free if there was no other option and, in a year or two, might have been found in a wild zone, happily chattering to each other as they surveyed for nopony at all. And for all intents and purposes, they forget that they have a daughter, for she is no longer hindering them by existing as a single additional thing to pack..."
Neither sister had their eyes open now. Positions were beginning to mutually, silently shift. "It's like falling. Only with no way to pull them out."
"Yes."
Falling into the mark: the most common psychological condition in Equestria. Nearly every pony went through a touch of it after manifest, spending some time being just a little too fascinated by new capabilities, and some just -- got worse. True falling took place when a pony stopped letting their mark guide their lives and allowed the talent to dictate. The majority simply never became interested in much of anything outside the mark's range. But for those who fell the furthest, the appearance of that condition... could sometimes resemble a lessened version of what the elder Releases had reached. Stay alive. Perform. Repeat. But with falling, a pony could be brought back by those who loved them. Full recovery for the deepest could take years... but it could still be done. And it never went as far as the Releases had gone.
"Which means," Celestia softly went on, "it may be almost impossible to find other cases, especially those in the early stages. Unless the doctors can isolate a factor which can be identified... so much of this is just going to look like falling. Find the common element in the blood or another symptom, and we can get them all together for study... but without that..."
"This disease," Luna quietly added, "may have been within our population for centuries. Falling itself might not be a condition of the mind, but one of the blood, and the disease has simply grown stronger with each generation..."
"Luna?"
"Sister?"
"It's bad enough already."
Which got her the faintest and falsest of smiles, unseen by closed eyes -- but felt. "Yes. Let us go through the lesser of the endings first."
It was time for that part of the worst-case scenario.
Celestia nodded. "A new contagious disease. Which we would have. We don't know how it spreads, if we've given it to others... but what we do know the onset time is gradual. Years."
"Of all those who could have first contracted it..." Luna softly said. "Where have they not been? Any portion of Equestria which they have not personally traveled to, those they have been in contact with would have reached. And -- you are overlooking something."
Celestia hadn't even remotely begun to overlook the small and potentially very final irony of what Luna had said, if 'irony' was even the right word: she personally felt the better fit was 'tragedy'. "What?"
"The onset time appears to be years for pegasi. How would it affect an alicorn body?"
The silence stopped all but heartbeats and breath. Those sounds would be the problem of another.
"I should have let myself be tested," Celestia sighed. "Centuries ago, and then over and over as medicine advanced. I should have found out everything about how our bodies work. If we knew... anything at all, anything beyond what we all figured out... but I just didn't want to be poked and prodded and sampled, and now..." But there was nothing to be done about that, and so the next part of worst stepped forward to take its proper order in the line. "Luna, if it's a case of active marks versus passive ones... ours are active."
"We could simply... find ourselves on our thrones," Luna told her, and the words which described the death of minds and souls were as gentle as any such could have been. "Not caring about the realm or our citizens or each other at all. Simply waiting for the next performance of our duty. Managing the burden. We would raise, we would lower, and we would remain alive. Perhaps during a moment of distraction, we might count down the time remaining or recite orbital velocities. New rulers would be needed -- but Sun and Moon would continue. For that if nothing else, the world would be safe."
"Or we might begin to make things move faster," Celestia whispered. "A gradual increase, one which wouldn't drain us -- but faster and faster over time, Sun and Moon whipping through the sky until every day and night were but seconds long..."
There were many things not said after that. Heat. Cold. Two new kinds of Nightmare as each half of the Diarchy decided her time was superior and had to rule over all. None of that needed to be said, for every possible form of sibling-created apocalypse was in both minds, and neither wished to hurt the other more than had already been done.
"But even for that, we likely have some time," Luna said, and there was caring in the words: there could have been nothing else. "You feel no such urges, nor do I. So, while we remain rational... let us discuss the arrangements. First, should we need to purchase additional days... cockatrice?"
Celestia wasn't seeing how that was going to help. "A shell of air-permeable stone with a little room left for ribs to expand -- but death would probably still come within a week, we've never exactly tested that, and while we were alive within, the disease progresses." Cockatrices liked their meat well-aged -- 'rotting' was the more appropriate word -- and in order to keep anything else from getting at it...
"But it would keep us from doing much of anything," Luna said -- and smiled. "A vacation, as it were..."
Celestia found a smile of her own somewhere, a weak specimen which had been cowering in a corner, hoping not to be noticed. It still proved up to the task. "True, but I'm not sure we'd be moving Sun and Moon either."
"We could test that." There was actually some mischief in the statement. "Who goes first?"
"We'll flip a bit. Rhynorn's Flu?"
They were still moving. Neither was fully aware of it.
"It is a disease of unicorns," Luna pointed out. "Neither of us have ever had it, and we have both been around those suffering from it. I suspect we may be immune. Again, this could be tested. Deliberate infection... which would purchase us about two weeks per bout of illness, at most. Only one at a time: somepony still needs their field fully available. But it only affects fields... not marks."
"Still..." It could at least slow down their ability to do anything with the increased urges.
"Still," Luna nodded. "When the time comes."
And then they were at the heart of it.
"When?" Luna asked, and deferred to her sister.
"While we're still rational," Celestia said. "We'll hang on as long as possible, but we have to be capable of performing the action without hesitation. Without turning away because we're thinking about something which we've decided is far more important..."
"It was always the last resort, was it not?" Luna quietly asked. "But until recently, you had no guaranteed way to make it work. Not without a new sextet of Bearers. We did not know what would break the prison and that method might not work again, not with the bindings having been renewed."
"I thought about it," Celestia gently told her. "While you were -- away. When a war was at its worst, if I thought there was a real chance of my death. That nopony would maintain the cycle. When Cadance... her magic is still so different, I'm not sure if she can and the pain the first time she tried, I couldn't force her to keep going... Luna, the way she screamed... But she would do it, if she could. I always knew she would make it work, if her magic allowed it at all. She would force herself through it, for the sake of the world. Except that..." Cadance had been exposed. The false last resort blocked.
"But he has not."
"I'm not sure he can even become sick. Flesh and blood is a choice for him, I've always felt that. And I've still been afraid to try calling on him for Joyous, because... he would think it was funny. He wouldn't help, or he'd just make things worse. He might spread the disease everywhere for the sake of the resulting chaos. And that's if... well, if we thought the chance of her talent operating on the shadowlands was bad..." They both shuddered. "And because... even if somehow, some way, we actually managed to convince him to help... it would have been pointless. We both know..."
Luna sighed. "The gap in his powers. Yes. We exploited it once. And now it works against us: I am certain he would appreciate the irony. But he still has all of his other abilities, and he demonstrated most of them during his brief release. He remains capable."
Celestia took the deepest breath of her life. "Then we're agreed."
Luna did the same. "Yes."
They had started the talk facing each other. Now they were not. Both bodies had begun to shift across the floor during the early part of the discussion, had continued to move throughout. The sisters were now parallel, mere hoofwidths apart.
"If there's no cure -- if we have the disease and it's certain that it will lead us to the point where we'll only destroy..."
"...we gather the Bearers. We give them an excuse, any excuse at all. That we need to question him on a matter, or perhaps we feel there is a possibility of reform." That produced a short, bitter laugh.
"They release him..."
"...and we turn the world over to Discord."
Their bodies pressed against each other in the dark. Feathers meshed.
"They'll hate us," Celestia said. "We'll be history's greatest traitors. Every generation to come will curse our names, any nation which partially survives his takeover spreading the tale of ultimate betrayal. But they'll be alive to hate us. He won't destroy everything, any more than he did before. He needs his audience..."
Luna nodded. Whispering, "The insanity... and here we are, at the point of wishing it on others. As the best thing we could ever grant them for our final legacy. After all we saw others go through, their losses, their pain, and... our..."
Pressing tighter now.
"They'll live," Celestia gently reminded her. "Some will."
"The damage," Luna said, and she was not talking about anypony, anyone, or any nation.
"It'll start building again," There was no help for that. "Maybe he won't have all that long to make it worse. They were healing... you felt that the first time you took it back, how much further along it was. It took... time for him to make things as bad as they were, at the point when we got control. I don't know how much time... that part of history is so clouded... but maybe... it won't accumulate too much. And as long as he controls them, they'll still work."
"We will need to hide the Elements," Luna realized. "Seize at least one immediately after the release, place them where none will make the discovery for a while. Buy him time. And as for... the rest..."
Celestia sighed. "I think we can get him to kill us. I wish I could say I was sure. He doesn't... repeat himself too often." Those words had barely emerged. "He might also think leaving us alive to do damage was funny, at least for a while. But if we can't provoke him that far, there's always the cockatrice..."
"It would be appropriate, would it not?" Luna proposed. "Statues for his garden."
"I remember the garden."
"Yes."
"It was..."
"Yes."
"Or... Luna, do you remember --?"
And the voice which answered was not entirely that of her sibling, who had always been skilled at imitation -- and that was not the whole of it. "'-- a triple corona around your horns. One strike each, a single moment of hard, sharp contact. Simultaneous. The backlash will hit -- and that will end it. Mutually assured destruction. If you two ever need it, for any reason... remember that. If there's nothing else I can still give you in life, then let me at least grant you the gift of a death...'"
Celestia smiled. Part of it was in thanks.
"I miss her," Luna said, and there was too much in the words.
"I do too."
"Will we see her, do you think?"
"Oh, yes. In the grass of the shadowlands. The family of our blood first, I think, because they've been waiting longer. But... right behind them, the family of our hearts. And I'll see... I'll be with..."
Luna's face pressed against Celestia's neck: the elder angled her eyes into the younger's mane.
The time required for the tears to stop might have been time they didn't have. But it was still necessary.
Finally, "There is one more detail, sister. One more... hope."
"Anything you have, Luna. Anything at all."
"Your student. If all turns towards the worst, until we know it can and will not do anything else... When we summon the Bearers, when we steal the Elements... we cannot come into contact with her. At all, ever again. She must remain untouched."
Celestia sighed. "It probably would have been time to bring her in for consultation, wouldn't it? But you're right... we can't directly expose her to anypony who might have been affected. Right now, my one consolation is that there is no disease which affects ponies and dragons. I don't think Spike's a carrier, but..."
"I walked within that dream, sister: there is no need to visit it again. But that is not what I was referring to. We can reach out to her in time from afar, if we must. We cannot let her know the full extent of our final plan... she would fight it and in doing so, perhaps keep it from being fulfilled. I meant..."
Luna swallowed, and a single extra tear flowed.
"...your other plan."
Celestia blinked.
"You've been yelling at me about that for nearly two years."
"Yes." A statement.
"You have protested every single step of the road."
"Yes." Fact.
"You have called me unreasonable, cruel --"
"-- among other things. Yes."
"And now you're supporting it."
"From this point forward. Even if it is in the blood, even if we find the cure for the disease. Yes."
"...why?"
"Because... she is the last hope. The only one on that specific road, the one we understand best, if that word can be applied to 'just barely'. The pony who matched us the most closely, whose situation could be likened to ours... whom the Elements might respond to. And with that potential additional factor -- you thought there was a chance..."
Celestia sighed. "I thought a lot of things. I don't know half of them. I was guessing, Luna. We spent decades together trying to backtrack the process, work out what the Elements were thinking. It took years just to remember any real parts of the talk, or that there was a talk at all. And then..."
Her own tear now, and she felt the nature of the mane it hit change, giving it something to soak.
"...I had time -- alone... I kept thinking about it, because... there were so many reasons. I know who she is, Luna. I know who she isn't. But at the same time... it felt like the chance was there. And part of it was... before you Returned..."
"...there was one," Luna quietly finished. "For centuries, there was but one. Cadance... her change must have lifted so much of the burden from you, knowing there was at least the chance of another once again. But she may share our doom..." there was shame in the words now "...and we should not dismiss her from our plans. I have been thinking of but two, when it should have been three all along. But... there must always be at least two, Tia, whenever possible. And if there cannot be two, when we have just found proof that even three may fall... the number should never be zero. Not for long."
Celestia nodded, but only slightly, for she refused to take her face away from the soft mane.
"You'll help me?"
"If I am able. But it is her road, and I am not among those who accompany her on the journey. Let us say... I will no longer consider standing in the way. There are still no guarantees that she will finish, but... the Elements are around her. The rest may happen. And it is cruel, sister, it is pain, it is something which I never would have gone through if not for the needs of the world -- and without you beside me. If I had been alone and possessed any level of choice while knowing what was to come... I would have gone through the change and wished for another all the while, a wish where I already know the thousand-year price..."
Both weeping now, with the smaller shaking, eyes squeezed shut as if they never wished to open again.
"I believe in your plan," Luna whispered. "I believe in the need, if perhaps not everything you felt had to go into the choice. To Discord, we give the true last resort..."
"In Twilight Sparkle," Celestia whispered back, "we place the last hope."
They stayed in the dungeon for some time after that, making lesser preparations, thinking of other things to be done in what time might remain while recommitting themselves to the fight which still could render every plan unnecessary. All except one.
The last words said before they left were "I love you."
And perhaps they had been said by each sibling in turn. One or the other might have spoken them first, or a chorus could have formed.
Ultimately, that did not matter either.