Yukiko Kumahira

Daughter of Hisashi Kumahira and Yumiko Hiyama. On the death of her father, her mother remarried to Alessandro Serpi's father: Marco Serpi. She was the victim of her adoptive father's experiments, who transplanted Magical Circuits into her body to make her the perfect sacrificial victim for the  Holy Grail of Yggdrasil's ritual. These tortures began when she was only twelve years old. Ten Magical Circuits were transplanted to her every month for the sole purpose of making her like Alessandro.
Yukiko was sacrificed at fifteen. The ritual failed and the man, struck by strong feelings of guilt, decided to put into practice an ancient ritual known as the Miracle of Eden to bring Yukiko back to life and make her a kind of doll: an Imitation.
Yukiko doesn't have a real soul, but rather a fake soul called the Mercurial Soul which can, therefore, contain an infinite number of Magical Circuits. The girl, immortal, eternally young and deprived of any form of empathy, decided to continue the transplant of Magical Circuits on herself.
The day she killed her father she had eight hundred and forty Magical Circuits.

With the false identity of Veronica Drakenberg, she started the Holy Grail War of Yggdrasil in London. She has committed several murders and caused the deaths of hundreds of thousands of people. With the help of a Berserker-class Servant (Artoria Pendragon) and the Grail she managed to destroy the entire universe, effectively causing the extinction of life itself. However, due to the nature of the Grail, everything started all over again and so Yukiko went to work to destroy everything a second time. She was stopped by Alessandro Serpi and Friedrich Wolff and later imprisoned in the Coven.
Yukiko is a sadistic girl who considers every human being as an object. She has no respect for life and she only craves one thing: the Void. Her sole purpose is to destroy everything in order to achieve the state of absolute nothingness. In her eyes, people have no freedom and are little different from things that can be used, destroyed and then forgotten. She appears to be physically unable to feel love, but she feels a strong sense of disgust towards humanity.

Artwork by BikoWolf