Movie
Description
Illyasviel von Einzbern is a Master participating in the Fifth Holy Grail War as the representative of the Einzbern family. She is a homunculus, an artificial lifeform created through alchemy, and the biological daughter of Kiritsugu Emiya and Irisviel von Einzbern. Her physical appearance is that of a young girl, with long silver-white hair and crimson red eyes, typically dressed in a purple long-sleeved shirt with a light purple scarf, a long white skirt, and purple boots. Despite looking like a child, Illyasviel is actually eighteen years old and is slightly older than Shirou Emiya. Her childlike stature is a result of extensive magical modifications made to her body before and after birth, which stunted her physical growth and halted the development of secondary sexual characteristics.

Illyasviel possesses an unsurpassed level of potential as a Master, with seventy percent of her body composed of magical circuits that also serve as her Command Spells, appearing as red patterns across her skin. She has an unlimited supply of mana, allowing her to control her Servant, Berserker, who is the legendary Greek hero Heracles, without significant difficulty. As a vessel for the Holy Grail, Illyasviel automatically absorbs the souls of defeated Servants, but her body can only contain four before she begins to lose her human functionality. She can create high-performance bird familiars called Zelle using single strands of her hair, a technique similar to the wire constructs used by her mother.

Her personality is a complex blend of cheerfulness, playfulness, and a disturbingly underdeveloped sense of morality regarding killing. She often exhibits an innocent and friendly demeanor, asking those she trusts to call her Illya, yet she can also be callous and cruel without remorse. This duality is inherited from her parents, as she has the kindness and childlike qualities of her mother Irisviel, but also the cold pragmatism of her father Kiritsugu. Her motivations are deeply rooted in her relationship with her father, who she believes abandoned her and the Einzbern family after the Fourth Holy Grail War to stay in Japan and care for Shirou, his adopted son. This perceived betrayal has fostered a deep-seated jealousy and desire for revenge against Shirou, whom she initially treats as both a target and a curiosity, calling him big brother.

In the Unlimited Blade Works storyline, Illyasviel travels to Fuyuki City and resides in the Einzbern castle on the outskirts, accompanied only by her Servant Berserker and her two maids, Leysritt and Sella. When Shirou Emiya and Rin Tohsaka later decide to form an alliance with her to confront the powerful Servant Caster, they arrive too late. Illyasviel is defeated by the Servant Gilgamesh, who kills Berserker after a fierce battle and then tears out her heart to use as the core of the Holy Grail, resulting in her death. Her key relationships are defined by her conflicting feelings for Shirou, whom she sees as an older brother figure despite her desire for revenge, and her deep bond with Berserker, who protects her and becomes a fatherly figure to the lonely girl.