Description

An honored guest of the Ryuudou family, permitted to live at their temple until the preparations for her marriage have been finalized. A gorgeous and talented yet mysterious woman of high stature, her presence has attracted the attention of many trainee monks.

<hidden by spoiler settings>She is actually a Caster-class Servant. Unlike other Servants, she does not have a weapon, but her rank allows her to manipulate Mana and perform magic like a wizard, something which other Servants cannot do.

[Edited from Wikipedia]