Dust of Osiris is the potential future version of Sion Eltnam Atlasia created from the remnants of Tatari, and a villainess from Tsukihime. She is the thirteenth of the twenty-seven Dead Apostle Ancestors after succeeding Night of Wallachia. She is voiced by Natsuki Rio.
Dust of Osiris is a version of Sion created from remnants of her soul by Wallachia after drinking three liters of her blood. These pieces of her soul developed correctly within Tatari over time and fought to seize Tatari's control system. It would have regularly been an impossible struggle, but she became the next generation Tatari after Wallachia was destroyed. She is a future representing the way things would have been if Sion had stayed with Atlas and eventually reached the position of chief of Atlas. She worked on creating the Philosopher's Stone to cure vampirism and revive Riesbyfe Stridberg, and also kept acting as an Eltnam while working on the prediction of the future for the purpose of protecting humanity from unavoidable destruction and the acquisition of a method of salvation from it. Having found no conclusion much like Zepia a millenium beforehand, she was eventually appointed as Tatari and one of the twenty-seven and sought to protect the future by destroying it herself and keeping an eternal record. She is brought forth one year after Night of Wallachia was destroyed by Arcueid Brunestud and Shiki Tohno, using her abilities to recreate events of the previous year, "Hologram Summer," once again in an attempt to form an even superior "Night of Wallachia." Her goal is to reach the future summoned by Arcueid to defeat Wallachia, out of belief that this is the "final and ultimate method of salvation" due to the fact that the self-destruction of humanity is unavoidable.
Osiris claims to lack emotions and ego, believing them to be what destroyed humanity, generally referring to everything with specific calculations, recalculations, and possible mental burdens as "processing slowdown." She only speaks to certain individuals that she encounters; otherwise, she simply continues with her calculations in a robotic fashion while preparing to destroy the intrusion. She believes she is the discarded human husk of Sion that was taken in by Tatari, and later developed into the "giant of Atlas," who differs from the vampiric remains of the real Sion who "degenerated towards humanity" and Sion TATARI who "degenerated into a demon." She believes the original Sion also seeks the same conclusion, as they split from the same person. She is surprised to find that Sion's interactions with Shiki have changed her and allowed her to see hope in the future.
The original will of Sion still exists within her, and she feels troubled after facing her own "worst possible condition" of Sion TATARI having embraced her vampirism. Interactions with Shiki and Ries bring about her true emotions, and surface the will of Sion that wishes for the destruction of Tatari and the prevention of the birth of an even superior Tatari. Shiki is called the "greatest singularity," as he directly identifies her as Sion. She finds this to be unforgivable, and claims that she represents a goodness that could potentially make her throw away the logic of becoming Tatari. Shiki mentions to Sion that she looked lonely, and she comments that her only saving grace was to be destroyed by him. After a fight with Ries, she returns to being Sion before her death, and apologizes to Ries for her actions. She believes herself to be a disappointment despite having been saved by Ries in the past, and that she is happy to have been killed by her.
Osiris has given up on a future that ensures humanity's survival, much like Zepia before her. She finds the idea of survival to be hideous, while believing the hollow outcome of destroying it and keeping an eternal record of her existence to be the only form of salvation. She sees herself as the "bird of the underworld that mourned the future and ceased holding hope in it," and a "prophet soaring through the end, together with Hermes." She isn't interested in anything else, wishing to destroy anything that brings no profit to the planet, such as Aoko Aozaki's magic. Wallachia finds her scenario to be greatly flawed despite the two having similar goals to one another. He claims that, while he lost his mind after discovering that there was no future where destruction was unavoidable, that she simply gave up. He calls her a wailing child that refuses to close the curtain by fleeting into the "method after" accepting that destruction was unavoidable. He finds they took polar opposite records to their conclusions, and despite having the same ending, that an end following the desperate struggle to live on is not a destruction but rather a conclusion.
Dust of Osiris is the final boss of a number of character scenarios in Melty Blood Actress Again. She is a non-playable boss character who, due to the sheer size of Hermes, a computing unit based on the pseudo spirit partical theory that she uses (also called the Moon Cell) which will keep all records of humanity eternally, takes up the majority of the screen in a similar fashion to G-Akiha and Neko Chaos Black G666. After being defeated in every scenario she's fought in, she disappears and reverts back to Sion, except in V. Sion's scenario where V. Sion absorbs her power.
Osiris is a Dead Apostle Ancestor, but she is no longer a true vampire after curing herself. She does not require the blood of humans to survive, having never harmed even a single person, and she lacks the transcendent pride and obligation that they generally display, instead choosing to abandon the choice of continued survival. After humanity is destroyed, she wishes to create a record of humanity in a medium that will never wear away. She believes ther is salvation in completely ceasing the furthering of humanity's history, and making a record that will never be destroyed or forgotten in order to give all life significance. Even with no one to view the records, the possibility of other beings learning from it remains. She uses Hermes, a computing unit based on the pseudo spirit particle theory, also called the Moon Cell, which will keep all records of humanity eternally. She refers to the processing unit as her main body.
The method of creating an eternal record is through the use of the Philosopher's Stones, the dust of the underworld transmuted using Tatari, and also called the Aqua Vitae, the water of life, that is the basic and the deepest-most part of alchemy and the greatest secret of Atlas able to heal all pain, plagues, and death. Initially created with the goal of curing vampirism and death, she will instead use them to power Hermes eternally. The ground has been turned into a blood-colored, gem-like substance that is made up entirely of lines of death when seen by Shiki. If she desires to speak to an intruder, she makes use of the Unified Language in order to speak with them. Individuals are disassembled and processed into living circuits the Philosopher’s Stones. Those with superior magic circuits like Ciel are preferable to reach her goal. With the crystallization of the planet and all of mankind into Philosopher's stones, the circuit of Hermes, after drinking them, will continually think of the assumption that humans still survive, even after mankind has died out and the planet has cooled. Arcueid claims this idea is one thousand years too late.
She has complete control over the abilities of Tatari, utilizing the gap from the changing of dates to shift the entire city of Misaki back one year to the "Hologram Summer" of Melty Blood. Only those involved within the events of the previous year experience the time slip, while normal civilians are kept within the correct flow of time. The memories of those present are also altered, causing them to forget most of the past year, believing Wallachia is the cause and forgetting that they have met Sion before, with the exception of the real Sion, Satsuki, White Len, Shiki Nanaya and Aoko. She also creates images of Michael Roa Valdamjong and Ries that were not present the year before as factors in the completion of her scenario. She displays the ability to "program" individuals, though they are not completely bound by those orders. Ries was to act as a defense mechanism, and was programmed not to approach her Hermes. She believes that the will of Sion before becoming Osiris is what allows her to deter from her role as a defense mechanism. Shiki is referred to as a singularity that made the reformation of the night possible, and he is a fluctuating variable that keeps the "answer", Osiris, and the world from being completed. She states that he is both a factor in creating and destroying her, and that before she is erased by the "correct answer", he must disappear in order for her to become the only Sion.
Osiris plans to plays the events of the reperformance of the "Hologram Summer" out exactly like Wallachia's scenario, which was one step away from attaining the Sixth, with the only difference being that she will recompute and correct the conclusion. After Wallachia is defeated, she has taken the future extracted from Arcueid's Marble Phantasm and deployed it in a way similar to a Reality Marble. She believes this future is the Black Land (黒い大地, ?), the etymological root of alchemy, and that it can be used to execute a better, swifter, form of annihilation compared to waiting for humanity to become extinct on its own. As a "mere smear on the world", she has taken it to bring about her desired future. It is the world showing the death of the planet in the future, where all life has become extinct, everything has been destroyed, and all has returned to dust. Following her goal of destroying humanity, she is using a great forbidden spell to seal reality in fantasy before Tatari dissipates. Following the world egg magical theory, once the world she created inside of the egg is completed, it will be switched with the world on the outside. Aoko comments that such a large ritual may attract the First Wraith, Stanrobe Calhin, to the city.
The beings brought forth by Dust of Osiris' calculations differ from those normally brought forth by Tatari. They are not made from rumors, but instead as a precise replication of the previous Hologram Summer. There are also those who were not present, such as Roa, created from the memories of the land, and Riesbyfe, brought forth by Dust to protect her. She can also control them to some extent if she programs their actions, but they are not absolutely bound to her. Those created still retain the autonomy allowed by other Tatari replications, meaning that they can attack or attempt to slay her if they so wish.