Illyasviel von Einzbern, often referred to as Illya, 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. Much like the other Einzbern homunculi, Illyasviel has crimson eyes and long white hair. Similar to her mother, Irisviel, Illya also bears a genetic resemblance to her ancestor, Justeaze Lizrich von Einzbern, who was responsible for the formation of the core of the Holy Grail. She wears a collared, purple long-sleeved shirt with a light purple scarf to match, a long white skirt and purple boots. Though Illya was born through natural means, her body has been heavily modified before and after her birth to maximize the magical circuits in her body, making her the ultimate homunculus and a refined vessel for the Holy Grail. As a result of the modifications to her body, her physical body develops slowly and her father, Kiritsugu Emiya, correctly assesses that her physical body will not develop secondary sexual characteristics. By the time she is eight years old, Kiritsugu notes that his Walther rifle is heavier than Illya is. A decade later, when Illya meets Shirou Emiya, she still looks as though she's a young girl rather than a young woman. 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". Illya's personal interest in Shirou is conflicted due to the fact that Kiritsugu, whom she loved for he was her father, remained in Japan as Shirou's adoptive father after betraying her family by destroying the long-sought Grail. She feels that Kiritsugu abandoned her for Shirou, and is jealous of Shirou for that. When she first meets Shirou, she considers him as something of an older brother. Though he is distrustful of her at first, he comes to like Illya, seeing her as a little sister. However at the same time, she also feels very close to Shirou for his relationship with Kiritsugu. As such, she becomes very affectionate and clingy towards him (like a younger sibling would) when Berserker is defeated, much to Saber and Rin's annoyance. While her personality got more unstable and cold-blooded due to the Einzberns' inhuman treatment of her, she keeps the kindness inherited from her parents deep down in her heart.