Illyasviel von Einzbern  (イリヤスフィール・フォン・アインツベルン, Iriyasufīru fon Aintsuberun?), often referred to as Illya[Note 2] (イリヤ, Iriya?), is the Master of Berserker in the Fifth Holy Grail War of Fate/stay night. She is the daughter of Kiritsugu Emiya and Irisviel von Einzbern, both whom participated in the Fourth Holy Grail War, and the adoptive older sister of Shirou Emiya.

Illya is cheerful and outgoing, upbeat and generally exhibits a positive attitude. Possessing a friendly demeanor, she is easy to talk to and tends to be playful and mischievous. Deep inside, however, Illya is lonely as she has no friends her own age to play with and is often stuck inside the Einzbern castle. She asks those she feels comfortable around to call her "Illya".