A serial-killer whose name is known all over the world. In Japan, it is often designated as "Jack the Ripper" without change. In spite of the frantic investigations of the Scotland Yard, it butchered five women and then disappeared without ever getting caught.

Because of this, Assassin-Jack was killed before even being born, her wish for the Holy Grail is a regression to the womb--to return to her mother's womb. Although ignorant of the ways of the world, maybe due to having been summoned as Jack the Ripper, she is frighteningly quick-witted.

She, who was summoned as Assassin, calls herself "Jack the Ripper"; but even she doesn't know if she is really the "true culprit". Although she has memories of killing several women, it is also unknown if they were Jack's victims

As a child that was never loved, she was strongly seeking out for love. Regardless of whatever the Master is male or female, she will probably demand his/her love as a "mother". While there is no problem in responding to that love, she might intend to sneak into your abdomen.

A ghost who might maybe not wear quite enough. She has a burning desire to dismember anyone who lets their guard down, even her own Master.