Miyu Edelfelt, originally Miyu Sakatsuki, is the "complete Holy Grail" from a parallel world where Class Cards were forged. Born into the occult-driven Sakatsuki family, which revered children under ten as deities, she grew up isolated with scant education or social contact, dependent only on her mother. Her innate power to grant any wish, mirroring the Holy Grail’s purpose, made her a target in the Fourth Holy Grail War. When a destructive shadow threatened Fuyuki, her abilities halted the disaster, attracting Kiritsugu Emiya, who sought to weaponize her power for global salvation, and Shirou Emiya, who formed a protective bond with her. After Kiritsugu’s death, Shirou became her adoptive brother, sparking her emotional evolution.

Her stunted upbringing left her stoic and hyperrational, struggling to prioritize empathy over logic despite her academic brilliance. Shirou’s influence softened her, culminating in her wish to become his true sister—a bond symbolized by her eyes shifting to match his. This choice unlocked her capacity for vulnerability and affection.

Kidnapped by Julian Ainsworth during the Fifth Holy Grail War, she was sent to Illyasviel von Einzbern’s world via Shirou’s wish. Adopted by Luvia Edelfelt, she embraced the magical girl role with Kaleidostick Sapphire, partnering with Illya. Their rivalry melted into a fiercely protective friendship, central to Miyu’s motivations. As a magical girl, she mastered Class Cards like Saber and Archer, battling threats like the Ainsworths, who coveted her Holy Grail essence. Captivity and encounters with figures like her parallel-world brother and Gilgamesh steeled her resolve to protect loved ones and pursue a future where all could be saved.

In *Fate/Grand Order*, summoned as a Caster by Ritsuka Fujimaru, her Noble Phantasm "Wish Upon a Star" channels tempered wish-granting power, reflecting her acceptance of destiny without surrendering humanity. Skills like "Unlimited Mana Supply" and "Willpower of the Little Girl" highlight her tenacity, even in lethal battles. Within Chaldea, her bond with Illya endures, while she navigates a wary rivalry with Chloe over Illya’s attention.

Miyu’s arc weaves identity, sacrifice, and redemption, tracing her shift from a sheltered instrument of fate to an autonomous individual. Her journey—from emotional detachment to fierce loyalty and hope—bridges her dual existence as both a magical entity and a girl yearning for ordinary bonds, anchoring her narrative significance across countless conflicts and worlds.