[b]Name[/b]: Ilyasviel von Einzbern ('Kuro')
[b]Age:[/b] ~13
[b]Gender:[/b] Female
[b]Appearance:[/b]
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[img]http://vignette1.wikia.nocookie.net/typemoon/images/8/83/Dark_kuro.png/revision/latest?cb=20140724145850[/img]
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[b]Canon, AU, or OC?:[/b] AU
[b]Universe of Origin[/b]: Fate/Kaleid Liner Prisma Ilya
[b]Personality[/b]: Ilyasviel is calm and nonchalant, analytical and able to pick up on an opponent's strategy. She is also devious and manipulative at the same time, whilst being brazen and unrestrained in her actions. These she uses in pursuit of her ultimate goal, which is survival first and foremost.

She is deeply bitter towards her parents for sealing her away, and to Ilya, for wanting to be normal. As a result, she will generally become infuriated by being considered secondhand or a clone. 
[b]Abilities/Weapons:[/b] Ilyasviel is the manifestation of the Archer Class Servant Card, and as such has many of the same abilities as Heroic Spirit EMIYA, including the ability to Project weapons and other Noble Phantasms, as well as physical objects. She also has the abilities of a magical girl, having the same physical strength while being an even more powerful magician due to having most of Ilya's magical power. 

Due to her existence, Ilyasviel is able to drain people of their prana to sustain herself, generally through kissing or other methods. She also has all of Ilya's memories, and the knowledge required to act as the key for the Holy Grail War.
[b]Backstory[/b]: 
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Kuro was born as Ilya von Eizbern, daughter of Irisviel von Einzbern and Kiritsugu Emiya. She was created to serve as the key for the Holy Grail War, and as such was given the knowledge that she would need to act as that key, far beyond that of a normal child. However, she would never be able to live out this purpose as Kiritsugu and Irisviel chose to reject the Holy Grail War, ending it before it could begin. Ilya's memories were suppressed, so she could grow up as a normal child, with no knowledge of magic. 

However, Irisviel miscalculated. While the memories were suppressed, and Ilya sent to live in Fuyuki, the personality she had locked away did not vanish. Instead it was sealed away and allowed to grow, a second personality inside Ilya that would stay hidden, even after Ilya encountered the magical world.

This side was eventually released during the fight against Saber, where the mental seal keeping her locked away was shattered. In that moment, the original personality reasserted itself, taking over her body and projecting Excalibur to ave the day. While it would be submerged, it would emerge twice more, once against the Assassins, and against Berserker.

The Class Cards had disrupted the flow of mana in the Earth, which Ilya went to fix with her partners. It was during this time that an immense reflux of magic takes place. With this energy and the fusion of the Archer class card, the original personality that had been unsealed so recently was able to separate itself from Ilya entirely, and create a new body. This new Ilya fled immediately afterwards, but returned he next day to launch multiple attempts on her counterparts life before being captured and named 'Kuro'.

Linked together so Kuro would feel the same pain Ilya felt, Kuro chose an indirect method, attempting to sabotage Ilya's normal life, but this fails. A discussion on motivation and Ilya's desire for a normal life left Kuro angry, and she ran away while preparing for the next round. It was during this next round that unleashed energy caused another reflux in the natural ley lines, which resulted in Kuro being thrown into a portal, whisked off to some far off world, much to her annoyance. Found somewhere unknown, she joined up with the people she thought could best help her - the Shadow Eternity. Now she works for them whilst looking for the opportunity to get back what she has lost. 

(Alternatively, Zelretch did it.)
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[b]Faction:[/b] Shadow Eternity