name: Illyasviel von Einzbern or simply Ilyaage: about 12 years old
nationality: German
profession: none
family: her maidens Leysritt and Sella who're looking after her.
likes: interacting with others, nature
dislikes: being considered a little girl
magic powers: She isn't a magician but she does posses impressive abilities.
servant: Berserker
personality: Ilya appears as a cute and innocent girl, although her words are cold and she looks like someone who isn't really interested in the life of others. She doesn't actually respect life at all, as she has somethign against humanity although her actions are only led by her personal resentment. Anyway although she's not very interested in the safety of those who're around her, and she tries to kill her opponents without mercy, she's not a mean person. She's always trying to make a positive impression on people, to take advantage of them, although sometimes she seems to get affectionated to those she's trying to manipulate (like Shirou of course, although she can't really decide what to do with him...she hates him for certain reasons, though she considers him as a big brother...this is a very twisted relationship!) She doesn't seem to be someone who can easilly forgive and she's very proud of her family's tradition. She actually is a lonely person who needs more attenction from others, although she doesn't directly asks for it. She has a strong bond with Berserker since he was the only one who was willing to do anything for her, who accepts her for what she is and not for what she represents. She's phisycally weak and she's pretty sure she couldn't live for long, for her conditions or maybe because of something she keeps as a secret.
spoilers warning!!!
personal story: Ilya belongs to the sorcerors family of von Einzbern, one of those who created the Holy War itself. She's none else than the Vessel of the Grail, or well the container which gaters all the energy that has to be transfered to the Holy Grail. Being the Vessel is part of her family's tradition and one of the basic requirements for the war itself.
She comes to Fuyuki City in order to take part ot the conflict and complete the Grail, punishing the heir of the person who betrayed her family, in the previous war, and destroyed the holy relic, and since that person is Shirou, she tries to take him down almost immediatly (although she prefers a fight with Rin, who's a more interesting adversary).
Her Berserker loses against Shirou and this was a very hard hit on her. She completly lost her will to fight and she got depressed as she though she was alone once again. But Shirou considers him a sister and tries evrything possible to cheer her up, asking also to Taiga to take Ilya with her.
Ilya eventually accepts the chance of beginning a new, peaceful life.
In the other scenarios Ilya is more friendly towards Shirou and his friends, although she always wants to win the war with all her means. In UBW she's killed by Gilgamesh (and the scene is pretty sad and malincholic, since she asks for Berseker's forgiveness for not being an excellent master)
and she's unable to realize her dream of being loved more. In Heavens feel she reveals herself as an humuncolous and that's probably teh reason why she could be a good Vessel. She freely decides to become the true Holy Grail, to helps Shirou out and to save him soul from complete destruction.
She dies, rejoining the Grail, but at least she gets the peace she was desperatly looking for.