Crafted by Kischur Zelretch Schweinorg, the Kaleidostick Mystic Code Magical Ruby grants its user magical girl transformations. Originally partnered with Rin Tohsaka, Ruby abandoned her due to Rin's constant conflicts with rival magus Luvia Edelfelt, deeming Rin unsuitable. Ruby then sought out Illyasviel von Einzbern, tricking her into a binding contract through manipulative steps, making Illya her new master and granting her magical girl abilities. Ruby's form features a yellow star within a ring, flanked by two small red beads and six white wings of descending size. A retractable red handle with a white top and gold cross at the bottom completes her design; this handle is absent when not wielded. While lacking a human form, Shirou Emiya visualizes her as a mischievous girl in a kimono. Personality-wise, Ruby radiates cheerfulness, mischievousness, and sadistic tendencies, frequently teasing or annoying her users. She openly expresses disdain for her creator, Zelretch, and relishes provoking reactions, such as referencing Illya's crush on Shirou or highlighting intimate dynamics between Illya, Miyu, and Chloe. Despite this, she demonstrates loyalty, especially to Illya, like warning her about the organ-damaging risks of using the mana-intensive Kaleido Liner Zwei form. This loyalty persists alongside her manipulative behavior, evident in her initial contract deception with Illya. Her core abilities derive from being a Second Magic mystic code. Ruby taps the Mana Plane to supply near-unlimited prana for sustained combat and transformations. She facilitates the "Install" function, allowing users to temporarily assume the abilities and traits of Heroic Spirits within Class Cards. Her capabilities also include flight, barrier creation, and combat support against adversaries like corrupted Servants or Bazett Fraga McRemitz. Across media, Ruby's role extends beyond the main series. In the Fate/Grand Order "Prisma Causeway" event, she and sister Sapphire accompany Illya and Miyu into a Reality Marble. Here, Ruby flees Connacht ☆ Medb, later analyzing Mash Kyrielight's potential as a Magical Girl. She assists the group in navigating the Reality Marble's challenges, battling Nursery ☆ Rhyme and Medical ☆ Medea while providing insights into the domain's powering jewels. In the OVA *Prisma Phantasm*, Ruby participates in surreal comedic segments. During the *2wei* season, she supports Illya and Kuro against Bazett, aiding in activating a protective seal to counter Bazett's assault. She later appears in a hot springs OVA where environmental mana depletion affects Kuro. Ruby's relationships include viewing Sapphire as her younger sister, frequently clashing with Rin over past grievances, and maintaining a protective yet teasing bond with Illya. She also interacts with Miyu Edelfelt during collaborative battles or parallel world events.