Irisviel von Einzbern, commonly known as "Iri," is a homunculus crafted by the Einzbern family. Designed as the prototype Holy Grail vessel for the Fourth Holy Grail War, her form echoes Justeaze Lizrich von Einzbern, complete with the family's signature silver hair and red eyes. Kiritsugu Emiya discovered her during creation, rescued her from abandonment in the Einzbern forests, and educated her about human society. This bond culminated in their marriage and the birth of their daughter, Illyasviel von Einzbern. Irisviel's pregnancy with Illya stemmed from an unplanned capability developed post-creation, marking her as the first Einzbern homunculus to become a mother. This experience profoundly shaped her emotional growth, enabling her to achieve human-like self-awareness and desires despite her artificial nature.

Within the *Fate/kaleid liner* timeline, Irisviel and Kiritsugu abandoned the Holy Grail War ritual when Illya was eight months old. To grant Illya a normal life, Irisviel sealed her daughter's preexisting Grail-related knowledge and magical abilities. This sealing inadvertently caused Illya's suppressed memories and original purpose to coalesce into a distinct personality, Chloe von Einzbern (Kuro), manifested via the Archer-class card. Irisviel formally adopted Chloe after mediating her conflict with Illya, offering her a place within the family.

Though frequently traveling abroad, Irisviel maintains a close connection with her family. She exhibits a consistently cheerful and carefree demeanor, often smiling regardless of circumstance. Her personality blends childlike curiosity with flashes of wisdom, reflecting her limited exposure to human life beyond Kiritsugu's teachings. She possesses a playful, teasing side, particularly directed at her adopted son Shirou Emiya, joking about his interactions with Illya, Chloe, and Miyu Edelfelt. She also notices and encourages romantic feelings others harbor for him, such as Rin Tohsaka and Luvia Edelfelt, once sharing smuggled photos of Shirou as "rewards."

Beneath her lighthearted exterior, Irisviel demonstrates perceptiveness and seriousness when required. She remains aware of Illya's latent connection to the Holy Grail and vigilantly monitors threats to her family. During the Eighth Class Card incident, she confronted Caren Hortensia regarding the anomalous Holy Grail ritual and later drove recklessly to locate Illya after detecting massive energy fluctuations. She maintains suspicion towards individuals with hidden agendas, like Caren's motives for observing the children.

Her abilities center on magecraft specializing in matter creation and forging. Her primary weapon involves flexible wires capable of transforming into constructs, such as a giant hand for immobilizing targets or shattering terrain. She also exhibits proficiency in healing magecraft. Her combat skills are secondary to a preference for evasion and negotiation, aligning with Einzbern defensive traditions. Notably, she is an infamously dangerous driver, treating vehicles as "toys" and disregarding traffic laws—a habit originating from learning solely within the Einzbern castle grounds.

Her role extends into the Ainsworth conflict within a parallel world, where she supports Illya's mission to rescue Miyu Edelfelt. Despite frequent absences due to travel, Irisviel's actions consistently prioritize preserving her family's daily life and safety.