Magical Ruby is a Kaleidostick-type Mystic Code crafted by Kischur Zelretch Schweinorg, functioning as a sentient magical device that enables magical girl transformations. Originally partnered with Rin Tohsaka, Ruby abandoned her due to Rin's constant conflicts with Luvia Edelfelt, judging Rin unfit. Ruby then tricked Illyasviel von Einzbern into a binding pact through multi-step deception to secure her as the new contractor. Her physical form resembles a toy-like wand featuring a yellow star encased in a ring, two small red beads, six descending white wings, and a retractable red handle with a white top and golden cross; the handle vanishes when inactive. Shirou Emiya subjectively perceives her as a kimono-clad mischievous girl, though this is not her true manifestation. Ruby's personality blends cheerfulness with manipulativeness and sadism. She persistently teases Illya about romantic feelings for brother Shirou, proposing ethically dubious tactics to "win" him. Despite this, she displays fierce loyalty, warning Illya about physical risks from advanced transformations like Zwei Form. She relishes provoking emotional reactions, such as highlighting Illya's intimate ties to Chloe and Miyu. Ruby openly scorns creator Zelretch while zealously upholding magical girl tropes, using them to critique Illya's hesitations or perceived shortcomings. In *Fate/kaleid liner Prisma Illya 2wei!*, Ruby orchestrates Illya's magical girl endeavors, facilitating mana transfers between Illya and her darker counterpart Kuro through comedic or suggestive framing. She advises during battles, like against Bazett Fraga McRemitz, aiding defensive seal activation. During *2wei Herz!*, she joins episodic escapades including beach outings and hot springs visits, noting the springs' mana-draining effect on Kuro and assisting investigations into related magical disturbances. Ruby appears in *Fate/hollow ataraxia* within Zelretch's Treasure Chest alongside Jeweled Sword blueprints. When Rin and Shirou become trapped, Ruby offers help but faces initial rejection from Rin due to past friction. Ruby provokes Rin into reactivating her, transforming Rin into "Kaleido Ruby" and triggering an embarrassing public encounter. During *Fate/Grand Order*'s *Prisma Causeway* event, Ruby and sister Sapphire transport with Illya and Miyu into the "First Lady"'s Reality Marble. After Miyu's capture, Ruby flees and encounters Mash Kyrielight, analyzing Mash's latent magical girl potential. She later guides Illya's group through themed kingdoms to gather crystallized emotion "jewels" needed to breach a magical barrier, providing tactical assessments like limitations in Illya and Miyu's dimensional travel and fluctuations in Mash's combat efficacy. Ruby's capabilities encompass dimensional travel, mana manipulation, and transformation sequences. Merging with Sapphire forms Kaleidostick Zwei, granting Illya enhanced powers while risking severe physical harm. Her analytical functions evaluate magical signatures and combat classes, exemplified when identifying Mash's Shielder class as a rare Heroic Spirit designation.