Miyu Edelfelt, originally Miyu Sakatsuki, is the hidden descendant of the "Child of God" (Kami Chigo) from the Sakatsuki family in a parallel world. Born a complete wish-granting Holy Grail, her isolated upbringing restricted education and human contact, leaving her initially unable to speak or read. During Fuyuki's Fourth Holy Grail War, Julian Ainsworth triggered a disaster destroying the Sakatsuki residence. Miyu unconsciously nullified the resulting black shadows, drawing Kiritsugu Emiya and his adopted son Shirou Emiya to rescue her. Kiritsugu viewed her as a tool, while Shirou formed a protective bond. After Kiritsugu's death, Shirou struggled to raise Miyu normally, confining her to the Emiya residence with non-practical education. On her tenth birthday, Miyu unknowingly activated her wish-granting ability to become Shirou's true sibling, changing her eye color to match his as proof. Shirou then accepted her as a sister, promising to show her the ocean. During a visit to the Sakatsuki ruins to explain her past, Julian Ainsworth intercepted them, kidnapped Miyu, and accused Shirou of theft. Shirou entered the Fifth Ainsworth Holy Grail War to rescue her, ultimately using the Grail to send Miyu to a parallel world for happiness. Occupied battling Angelica Ainsworth in his Reality Marble, Shirou couldn't accompany her, leaving her alone in the new world with Class Cards and a Holy Grail ritual circle. Arriving in Illyasviel von Einzbern's world, Miyu was found by Luviagelita Edelfelt (Luvia), who sought a partner to rival Rin Tohsaka and Illya's alliance. Miyu negotiated adoption into the Edelfelt family in exchange for aiding Luvia in collecting Class Cards using the Kaleidostick Magical Sapphire. As part of the household, she attended elementary school, wore the standard uniform, and lived in a mansion Luvia built opposite the Einzbern residence. Miyu initially displayed a mature, stoic, and emotionally distant personality, prioritizing her magical girl duties with ruthless efficiency. Her upbringing granted advanced physics and mathematics knowledge but underdeveloped social skills, causing her to assess situations logically, not emotionally. She dismissed Illya's abilities early, viewing her as a rival. However, collaborating to collect Class Cards gradually opened Miyu up, forging a deep, protective friendship with Illya central to her character. She frequently stated hardships were manageable "if I’m with Illya". She also developed a rivalry with Chloe von Einzbern over Illya's affection, reacting coldly to Chloe's flirtations. Her personality split into two facets: affectionate and devoted to trusted individuals (Illya, Shirou, Luvia), yet cold and dismissive towards others. Around Shirou, she exhibited childlike tendencies like wearing animal-themed pajamas, seeking affection, and throwing tantrums. Reuniting with him during the Ainsworth conflict made her noticeably more expressive and playful. Her time with Luvia fostered a sisterly dynamic, with Luvia providing guidance and protection. As a magical girl wielding Magical Sapphire, Miyu gained flight, energy beams, force fields, and dimensional travel to the Mirror World. Her combat style emphasized logic and precision, contrasting Illya's instinctive approach. She mastered "Install" early, using Class Cards to temporarily assume powers and outfits of Heroic Spirits like Saber (without chest armor), Rider (mirroring the original), and Archer/Gilgamesh (exposing her abdomen). Her Noble Phantasm in Fate/Grand Order, "Wish Upon a Star", reflects her Grail origins. As a Holy Grail, she could unconsciously grant wishes, as seen when altering her relationship with Shirou, though this required sacrifice and invited exploitation like the Ainsworths' plan to evolve humanity. In "Licht - The Nameless Girl", Miyu was imprisoned by the Ainsworth family in her original world, forced into a ritual to reshape humanity. Julian Ainsworth, possessed by Darius Ainsworth, threatened Shirou's life to coerce her cooperation. During captivity, Erika Ainsworth attempted friendship; Miyu initially rebuffed her before reluctantly sharing stories about Illya. Her rescue involved Illya and allies navigating parallel worlds and confronting the Ainsworths, culminating in a battle deciding Miyu's safety and the fate of multiple worlds. Her design features long black hair in low pigtails, golden-brown eyes, and a petite stature. Her magical girl outfit is blue-and-black with a white cape and boots; Class Cards are stored on her left leg strap. During Ainsworth captivity, she wore a revealing black dress; as the Grail vessel, she donned a black babydoll dress shaped like a cross.