Koyanskaya

Koyanskaya, true name Tamamo Vitch, is one of the three secondary antagonists in Fate/Grand Order: Cosmos in the Lostbelts (alongside Kirei Kotomine and Caster Limbo), being a voiceless minor character in Moon/Lostroom OVA, the main antagonist of its prologue chapter and a supporting antagonist in the following chapters.

She is, as far as we know, an Alter Ego-Classed Servant who serves the mysterious Alien God and assist the Crypters to destroy the Pan-Human History, but her role stays ambiguous as she always sabotage the Crypters' project and caused their downfall, successfully bringing down Kadoc Zemlupus and Ophelia Phamrsolone indirectly, making every remaining Crypters to be wary of her.

In addition, her Servant Form shows eerie similarity to the Lostbelt Assassin from the promotional trailers, though it's yet to be officially comfirmed that they are the same Servant.

If the above information is comfirmed, she will be voiced by Chiwa Saito, who also voiced Tamamo-no-Mae and her counterparts in Fate series, Homura Akemi in Puella Magi Madoka Magica, Nureha in Log Horizon, and Kokoa Shuzen in Rosario + Vampire.

SIN: The Land of Unified Knowledge
After the destruction of Norse Lostbelt, Kirschtaria summoned the remaining Crypters for another meeting, including a defeated Kadoc, who remained in Kirschtaria's Lostbelt. During the meeting, Koyaskaya arrived and started her pretentious weep for the demise of Ophelia.

Disgusted, Hinako Akuta called out Koyanskaya as the latter's mourning was fake, claiming she was even more disgusting than the problems caused by Chaledea. Blaming Koyaskaya as the reason for Kadoc and Ophelia's downfall, Hinako also stated that she was relieved that Ophelia died so that Koyanskaya wouldn't got her Mystic Eye as a collection.

Irritated, Koyanskaya talked back at Hinako and satried her uncaring attitude towards Ophelia, causing Hinako to get enraged and lashed out at the fox-human, revealing sharpened fang inside her mouth. Before a fight could ensued, Scandinavia Peperoncino stopped them from quarreling, before bluntly stating his sadness over Ophelia's passing.

After both sides were settled down, Peperoncino then proposed a funeral attempt for Ophelia. However, Hinako rejected an idea of funeral, saying she already prepared a bunch of flowers to mourn Ophelia. Then, Hinako left for the Chinese Lostbelt, but not before she stated to Kirschtaria that she never wanted Koyaskaya to enter her Lostbelt ever again.

Using teleportation via her Skill of Independent Manifestation, Koyanskaya later arrived at the new Chaldea now situated at the Wandering Sea, using the lipstick she gave to Godolf to track him down. She later poisoned Ritsuka and Godolf while the Chaledea Crew were planning to attack the Greek Lostbelt around Atlantic Ocean. Due to showing resistance to toxin, Ritsuka was just have mild discomfort but without risk of life. Nevertheless, Godolf's lifespan was shortened into ten days and could only be saved by Koyanskaya's antidote.

After she escaped, Koyanskaya directly went into the Chinese Lostbelt, against Hinako's will, while Godolf was in sheer disillution that Koyanskaya used her lipstick as her gift to him only trying to track him down. The Chaldea crew was forced to change target and went into the Chinese Lostbelt.

Upon listening up to the news, Hinako angrily berated Koyanskaya, who was rather surprised due to the Chaldea crew's presence. Hinako tried to warn Emperor Qin Shi Huang, the King of Chinese Lostbelt based on the first Emperor of China, about Chaldea. In the meantime, Koyanskaya sent creatures from other Lostbelts into fields to attack people constantly, and was always annoyed that the Emperor cannot pronounce her name correctly.

At first, the Emperor ignored the news of Chaldea's arrival, trying to be friendly towards them, until he discovered that Jing Ke - his historical archenemy - was teaching people reading and writing poetry. Considering it to be an act led by the Confucianists, people whom he hated the most, the Emperor ordered Qin Liangyu, one of his Lostbelt Generals, to take away the Shadow Boarder and arrested Holmes, Da Vinci and Godolf by force. In the meantime, he arrested Koyanskaya and put her under imprisonment after finding out the beasts that was attacking his people.

While being chained inside the jail, Koyanskaya was visited by Hinako, who claimed she had it coming and ignored her pleadge. She was then visited by the Priestess of the Alien God once more. Bitterly, Koyanskaya told the Priestess about how conservative Qin Shi Huang was. However, her words was overheard by the Emperor, who asked if she was talking to herself like crazy (due to the Emperor cannot see the Priestess).

As the Priestess silently left, the Emperor sent robots and put Koyanskaya into severe and constant torture, saying she had weighed a lot more than usual Heroic Spirits, much to his surprise. Koyanskaya pleadged to be spared and swore to leave Chinese Lostbelt, but the Emperor refused, saying she would go to other realms and wreck havoc if he released her. He then said Koyanskaya would rot in her prison for eternity before he left, leaving Koyanskaya shireking in agony.

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Trivia

 * LostbeltAssassinTamamo.pngskaya, especially in her Chinese-styled attire, appears similar to the Assassin used to promote the Cosmos in the Lostbelt, but they are not yet confirmed to be the same person.
 * There is a common theory that Koyanskaya is actually a Beast of Calamity due to showing the Skill of Independent Manifestation, a Skill which is normally restricted to the Beast-Class Servants like Goetia, Tiamat and Kiara Sessyoin (even in her Alter Ego form), and potentially Heroic Spirits that qualify as Grand Servants (like Merlin, Solomon and Shiki Ryougi (Saber)).
 * In addition, while torturing her, Emperor Qin Shi Huang commented that Koyanskaya, as a Heroic Spirit, has tremendous and unprecedented weight, much to his surprise. Koyanskaya only replied with a death glare and an evil grin, possibly hinting that the Emperor's speculation was true.