Illyasviel von Einzbern exists in an alternate timeline where her parents, Kiritsugu Emiya and Irisviel von Einzbern, abandoned the Fourth Holy Grail War and dismantled its ritual. This choice allowed her an ordinary childhood in Fuyuki City as an elementary school student alongside her adopted brother, Shirou Emiya, cared for by the Einzbern homunculus maids Sella and Leysritt. Unlike counterparts in other timelines, she possesses a cheerful, shy, and relatively innocent personality, untouched by the Holy Grail War's trauma. Her creation involved Einzbern modifications to serve as the Holy Grail vessel, embedding knowledge of magecraft and the Grail system. At eight months old, her parents sealed these memories and her magical abilities, inadvertently creating a separate personality that later manifested as Chloe von Einzbern. Her life transformed when the sentient Kaleidostick Ruby, originally meant for Rin Tohsaka, selected her as its master, turning her into a magical girl. Tasked with collecting seven Class Cards containing corrupted Heroic Spirits, she reluctantly battled across Fuyuki. During this mission, she encountered Miyu Edelfelt, who became both rival and close friend after contracting with Sapphire. Their partnership evolved as they worked together to retrieve the Cards, facing threats like the manifested Caster under Fuyuki Bridge. This period marked her initial growth from a reluctant fighter into someone willing to protect others, though she struggled with fear and self-doubt, especially after nearly harming allies during a berserk state. The emergence of Chloe von Einzbern complicated her existence. Chloe embodied Illyasviel's sealed memories and original Grail vessel personality, now independent and physically sustained by Illyasviel's mana. Initially adversarial, their relationship shifted when Irisviel intervened, revealing Chloe's origins. Illyasviel accepted Chloe as a sister, regularly supplying her with mana through kisses—a necessity due to Chloe's inability to generate mana independently. This dynamic highlighted Illyasviel's capacity for forgiveness and familial bonds. Further challenges arose with an eighth Class Card, Gilgamesh, who revealed Miyu's origin as a parallel world's Holy Grail before absorbing her. To rescue Miyu, Illyasviel combined Ruby and Sapphire into the Kaleido Liner Zwei form, gaining cosmic-like wings and enhanced power at great physical cost—her internal organs suffered damage from channeling excessive mana. Later, after Miyu's kidnapping by the Ainsworth family, Illyasviel traveled to a parallel world, teaming with allies like the amnesic Tanaka, Gilgamesh, and Miyu's brother Shirou. Confronting the Ainsworths' plan to exploit Miyu as a Grail, she demonstrated resilience and strategic ingenuity, such as using Saber and Caster card abilities simultaneously against Darius Ainsworth. Her personality balances youthful innocence with conflict-earned maturity. She retains traits like a fascination with maid outfits, a covert interest in romantic scenarios, and a strong attachment to Shirou, though less clingy than in other timelines. Her relationships are central: with Miyu, she shares a deep, pseudo-romantic bond; with Chloe, she embraces a protective older-sister role; and with allies like Rin Tohsaka and Luvia Edelfelt, she navigates mentorship and rivalry. Her optimism and refusal to abandon others define her heroism, exemplified by rejecting a Sadistic Choice to save either Miyu or the world, insisting on saving both. In the OVA "Prisma Phantasm," a comedic spin-off, her role is limited. The narrative primarily focuses on other characters, with Illyasviel appearing only in the final segment alongside Chloe, engaged in lighthearted, non-canonical scenarios referencing her magical girl exploits. Her abilities evolved significantly. Initially reliant on Ruby for basic barriers and flight, she mastered Class Card Installations, accessing powers of Heroic Spirits like Archer (projecting swords such as Kanshou and Bakuya) and Saber (channeling Artoria Pendragon's "Princess Knight" aspect). Her Zwei form represents her peak capability, albeit hazardous. Later innovations include Include, a partial card activation for specific abilities without full transformation. These skills, combined with her innate mana reserves as a former Grail vessel, enable feats like reality-warping projections during her "Kaleid Trance" state, though her physical fragility remains a limitation.