Aozaki. A name that appears briefly in the story. It is the family name of the magi who manage the most outstanding “spiritual lands” in all of Japan.
In the world of magi, they are synonymous with trouble.
Their lineage is an old one, yet they are not a distinguished family. However, due to the “road” opened by one of the family heads, the Aozaki successor has a high chance of inheriting the title of “magician.”
In the current generation, the candidates for next family head were an inauspicious pair of sisters, and when the dust settled after their bloody battle for succession, the younger sister had become a magician.
The older sister went to London and made quite the name for herself, but something about life there must have disagreed with her because she soon broke ties with them and went her own way.
During the events of Fuyuki’s Fifth Holy Grail War, the older sister was busy concealing her whereabouts, while the younger sister was touring around Japan without a care in the world.
Also, though the younger sister is only capable of destruction, the older sister is a genius who’s skilled at just about everything. It seems she may even have a small role in the story of Fate/stay night, too.

Fate/side material: Fate Encyclopedia