Irisviel von Einzbern

Irisviel von Einzbern is the partner of Saber as well as the intended vessel for the Holy Grail. She is the mother of Illyasviel von Einzbern, who was modified in her mother's womb to be homunculus, a being with a human appearance but is composed of a cluster of magical circuits. Like her daughter, Irisviel is a homunculus, an artificial being created by the Einzbern. She was raised to be a puppet with no desires, but found happiness in her existence when she gave birth to Illyasviel.

Role
While she and Saber work together, Saber's master is actually Emiya Kiritsugu, the Einzbern family's representative in the war who acts independently from his Servant and arrived in Fuyuki City without her. Irisviel has been entrusted with the role of becoming the vessel of the Holy Grail and acts as Saber's healer and supporting partner while Kiritsugu works with his assistant, Hisau Maiya.

Irisviel is innocent and carefree, which results from living her entire life without leaving the Einzberns' castle in Europe until the beginning of the Fourth Holy Grail War, in which she leaves for Japan with Saber. Due to her secluded and isolated upbringing, she is unusually fascinated with Fuyuki City and openly explores the city with Saber as her escort during her first day. Her carefree nature extends to her relationship with Saber, where Irisviel chooses what clothing Saber should wear. The two get along well and become friends to the extent which Saber is willing to tell the story of her past to Irisviel.

Despite the way Irisviel acts, she displays a mature attitude and understanding towards Kiritsugu and the agony he suffers as well as the knowledge that she will likely die in the war because of his actions. She also tries to present Saber with a better impression of Kiritsugu since Saber feels her Master's cold nature derives from his belief she is unsatisfactory as a Servant because she is female.