Fragmentary Record(Dust of Osiris)
Our final foe, barring the return of Wallachia, is a being - or in this case, two beings - called the [Dust of Osiris]. It is a Spirit of sorts, but not in the sense that the world of magecraft understands it - and, I can see I have lost you already. Allow me to restart.
-Of the two hundred and thirty-four worlds simulated by Quasar, assorted beings referring to themselves as the Dust of Osiris emerged in one hundred and fifty-nine of them. But these beings had nothing in common with each other - certainly, in some worlds, the same person might declare herself the Dust, but the circumstance of emergence was almost always different, and her objective, abilities, and desires could range wildly.
In short, the title [Dust of Osiris] means nothing, magically speaking. It is a title, chosen by unrelated individuals, across unrelated worlds, holding only two things in common. The first, that the one to claim the title will be an intelligence of some sort associated with the Atlas Institute. The second, that the Dust shall have decided it to be expedient that the Atlas Institute should perish so that humanity might live.
In that sense, it is a spirit of sorts - not in the sense that the world of Magecraft would understand, but a spirit nonetheless. If one peruses the annals of western esotericism, they might come across the idea of an [Egregore] - a spirit born from the common minds of a population - and the majority of mages of the Clock Tower believe that this is a primitive, superstitious understanding of the nature of mystery!
And yet, the Dust of Osiris is born. A possessing spirit, without any mystery, purely psychological in nature. Proof that things like [Possession] and [Thought Magecraft] are indeed [Magecraft], for their effect can be produced without any use of the supernatural.
Put more simply, the [Dust of Osiris] is a sort of cultural meme, which will always emerge from the collective unconscious of the Atlas Institute, given enough time and pressure. The inevitable reality that, among hundreds of mad alchemists, one will eventually stand victorious, sacrificing the rest of her colleagues to avert her personal vision of the apocalypse.
***
"So the title doesn't mean anything?" Natsuki Subaru asks. "What was the point of that whole rant…?"
I feel a slight twitch of anger. "It matters with regard to the culture of the Atlas - no, I suppose you would not care about such things. It's my fault for casting pearls before swine."
"O-oi! Come on, would it kill you to be even a little nice!?" Natsuki Subaru groans.
***
-This time, the [Dust of Osiris] consists of two individuals in pursuit of a single goal. An insane method to 'save' mankind without defeating the King of Demon Gods. If I had to describe it simply, their method is as follows: "If the 'minds' of humanity survive, then isn't that as good as humanity surviving?" An insane belief, one only the special madness of those people who were born in the twenty-first century could produce. Only a person completely alienated from his [Body] and [Soul] can believe that [Mind] is all he is.
To put it even more directly, their scheme is to read all of the billions of books of the dead currently stored within Taygeta - and, having done so, the hallucinations they have given themselves will suffice to serve as the future of humanity. Needless to say, this is delusion - a [Record], no matter how perfect, is not the same as a life! The hallucinations produced by reading the [Books of the Dead] are just that - hallucinations! But the two-headed bird of Hades has already fallen into delusion.
That boy, [ ] has every reason to choose to believe it, to give himself over to the madness of believing the people he murdered are still with him. His master, Sion Eltnam Sokaris, fell into the same delusion while attempting to utilize her [Etherlite] to probe his mind. From that point, her precious calculations become absolute junk, as they are based on false observations.
***
"Sion!?" Natsuki Subaru shouts in agitation. "Seriously!? No, I get that she was a little kooky, but she's gotta be at least be a bit smarter than that!?"
"The people of Atlas focus upon the mind entirely - their craft requires it. But as a result, they are much like those people living in the so-called 'first world', the despisers of the body who, disassociated from their flesh by technology, come to think of themselves as minds and souls attached to a body. But, as the sage wrote, 'Body am I entirely, and nothing more; and soul is only the name of something in the body.'" I say, shaking my head. "Her endeavor is pure folly."
{Look, I get why Nietzsche appeals to your sensibilities, but his view on that is pretty much the opposite of true…} My Master complains. {If anything, Body and Mind both proceed from the Soul.}
"-Okay, so… Sion is here. Is she a Figment inherited from the previous Tatari, or…?" Natsuki Subaru asks.
"No. The Sion Eltnam Sokaris who emerged here is none other than the same vampire who exists in the real world. The rumor invoked was 'a vampire's ability to regenerate' - I suppose some holdover of the true Zepia caused the false one to save his granddaughter's life," I reply.
"-Wait, so does that mean-!?" He begins to say, but I scowl in response.
"That you can recruit her? Do not be naive! That girl has already lost her mind! There is no future for her but death," I shout. "Do you wish to appeal to her through your shared history!? Do not forget that your friendship with her has not occurred!"
His eyes widen. "You-"
"Of course I am aware of [Return by Death]. My records encompass all things," I huff. "Don't speak about it, and certainly not outside of my Reality Marble."
"No, but…" His face falls slightly. "I feel like-" Honestly, this man is infuriating.
"Would you ask that I praise you? That I feel pity for you? That I search for a way to shelter you from your own Authority?" I ask, resting a hand on my hip. "I have nothing to say on the subject. I have known of it from the beginning, and it holds no relevance for me. In every scenario except the worst, it is inferior to my records, and in such a case, its fruits will simply be added to my records whether I wish it or not."
Natsuki Subaru falls silent for a moment, opening and closing his mouth. I suppose this is his first time witnessing complete apathy towards [Return by Death] and the suffering it inflicts.
"-In any case, I have no intention to make use of your Authority. It serves only as a liability, so far as I am concerned," I conclude. "And of course, a potential obstacle, so far as the Figment bearing your face is concerned."
He looks, hurt for a moment, then upset - then, breathing deeply, Natsuki Subaru closes his eyes, and when they open again they are attentive. "-Is he actually a Figment? Or are you just saying that to make things easier?"
"It's the truth," I answer. Though, from the look in his eyes, it seems he doesn't believe me… how irritating. "Stop trying to think for yourself, Natsuki Subaru. You're terrible at it."
"Then give me some kind of reason to believe in you! Make a contract with me, or something! You've been playing everything so close to your chest this whole time, but how am I supposed to trust you on this if you keep hiding things!?" He shouts.
"A contract with you would only cause problems at this stage," I reply. "My current Master has far more ample mana reserves, and you need to retain your mana to provide for yourself and your fellow combatants in the tower."
"So you have another Master, even!? Who even-"
"Merlin, the Mage of Flowers, is the one who summoned me to Chaldea. From his tower in Avalon, he has been observing your exploits for all this time; he already hacked into Chaldea's systems to provide backup mana during the Fuyuki incident, and so it was possible for him to summon me here for this incident," I say. If it can buy back some credibility, that will make things far easier.
"I don't suppose it occurred to him to send someone more trustworthy?" Natsuki Subaru asks sullenly.
A small growl leaves my lips. "Disbelieve me if you wish. I will simply plan around you."
"Even Nee-sama was less abrasive than you, seriously…" He mumbles.
***
Regarding the Figment produced by Sion Eltnam Sokaris's summoning within the Pleiades watchtower, he in some sense needs no introduction. His identity is one you are familiar with - a what-if, of a Natsuki Subaru who, after his memories were devoured by Louis Arneb, sought to piece together a facsimile of the now seemingly invincible "Natsuki Subaru" who had been there before.
Following his reading of Meili Portroute's book, he hatched a mad scheme - simply put, he would kill his companions, read their Books of the Dead, and learn the secret of "Natsuki Subaru." Of course, no such secret existed; the issue at hand was simply his own self-esteem and the fact that he was unaccustomed to suffering. But when he could not find the secret among his companions at the Watchtower, he took it further. That boy - let us call him Algol, after the demon star. Once Algol had murdered his companions, he set forth from the watchtower, with Shaula as his sole companion apart from the voices in his head. And, from that day forward, he roved the world, murdering every person who had the misfortune of knowing "Natsuki Subaru", never once doubting that at the end he could simply [Return by Death] to the world where the people "Natsuki Subaru" loved were still alive. Or perhaps he even knew that he could not return, and at that point he had already become the first head of the Dust of Osiris.
…As I have said, he is a figment. His class is Rider, and his Noble Phantasm is the Scorpion named Shaula. Neither she, nor the hallucinations you experienced while within the tower are 'real', and once the dawn comes, they shall vanish as smoke vanishes on the wind. You should make your peace with that now.