OVA
Description
Illyasviel von Einzbern lives in Fuyuki City as an elementary school student with her adoptive brother Shirou Emiya and maids Leysritt and Sella, while her parents Kiritsugu Emiya and Irisviel von Einzbern remain frequently abroad. Originally created as the Holy Grail vessel for the Fourth Fuyuki Holy Grail War, her parents abandoned the ritual when she was eight months old. Irisviel sealed Illya's magical abilities and war-related memories to ensure a normal childhood, suppressing her original personality and knowledge. This sealed persona later manifested as a distinct entity named Kuro.

Her personality blends cheerfulness, innocence, and initial shyness, differing from her callous counterparts in other timelines. She displays typical elementary school interests like anime fandom and adoration for cute animals, alongside a covert fascination with maid outfits. Magical Ruby frequently highlights her precocious crush on Shirou, causing embarrassment. Illya forms a close bond with fellow magical girl Miyu Edelfelt, showing protective instincts and a desire to share everyday experiences such as meals and baths. Her capacity for forgiveness extends to forming relationships with former enemies like Chloe (Kuro), Bazett, and Angelica.

Her development starts when the sentient Kaleidostick "Magical Ruby" selects her as its master, abandoning Rin Tohsaka. Tricked into a contract, Illya gains magical girl abilities. Tasked by Rin to collect dangerous Class Cards—artifacts containing Heroic Spirits disrupting Fuyuki's leylines—she initially faces reluctance and fear. Traumatic battles, like nearly killing allies while defeating Saber Alter, trigger self-doubt. Her mother Irisviel helps her overcome this crisis, reinforcing her resolve to protect others. She evolves from a passive participant to a determined heroine, vowing to save both Miyu and the world despite being told it is impossible.

Key conflicts deepen her growth. During a leyline-sealing operation, she splits into two entities, causing the emergence of Kuro—her suppressed grail-vessel persona. Initially antagonistic, Kuro experiences an existential crisis over lacking purpose, culminating in Illya sharing her mana and accepting her as family. When Miyu is abducted by the Ainsworth family to an alternate world, Illya pursues her, navigating parallel realities and allying with figures like Gilgamesh and an alternate Shirou to mount a rescue.

Her magical abilities derive from Ruby, granting flight, barrier creation, and Card Installs—temporary transformations into Heroic Spirits using Class Cards. Early installations include Archer (wielding twin swords Kanshou and Bakuya) and Saber. A significant power is Kaleid Liner Zwei, achieved by merging Ruby and Miyu's Kaleidostick Sapphire. This form grants cosmic-themed wings and immense power but damages her internal organs when used as pseudo-magic circuits. Her latent connection to the Third Magic, as a potential Holy Grail vessel, enables limitless mana during her "Kaleid Trance" state, though sealed memories limit conscious access to this power.

Her journey includes confronting the Eighth Class Card, Gilgamesh, who reveals Miyu's origin as a parallel-world Holy Grail before absorbing her. Illya defeats him using the Zwei form, though Miyu is later kidnapped. In the parallel world, she allies with Tanaka (an amnesiac) and a captive Shirou against the Ainsworths, facing Angelica and Beatrice Flowerchild. Her resolve solidifies in protecting allies and challenging adversaries like Julian Ainsworth. Physical transformations occur during Installations, such as her Saber form manifesting a "Princess Knight" aspect instead of Artoria Pendragon.