Ruler / Jeanne d’Arc
She is a governing Heroic Spirit summoned by the Great Grail to oversee the Holy Grail War.
Her true name is Joan of Arc.
At first, she was thought to have been called forth to run the greatest Holy Grail War without delay, but she presently takes notice of the conspiracy behind the War.
Jeanne d’Arc x Jack The Ripper
I remember talking with my friend Tessarossa many years ago about Fate and she mentioned possibility of Jeanne appearing one day. Looks like someone had the same idea.