Mash Kyrielight is a genetically engineered human forged by the Chaldea Security Organization for the Demi-Servant project, designed to fuse with a Heroic Spirit. Her creation involved artificial fertilization and genetic editing, resulting in a predetermined lifespan of 18 years. By her involvement with Chaldea's main operations, she had lived 16 years, hurtling toward its predetermined conclusion. Initially designated "Summoning Experiment #2," she later received her full name and assignment to Team A. The project successfully bound her with the Heroic Spirit Galahad, though he refused to awaken or cooperate after witnessing the brutal experiments she endured. Galahad remained dormant within her to sustain her life but withheld his identity and powers, intervening only at critical moments. Physically, she possesses short lilac hair, lavender eyes, and fair skin. Her Demi-Servant augmentation maintains her body at peak physical condition, preventing visible aging. Casually, she wears rectangular glasses, a grey hoodie, a black shirt layered over a white-collar shirt, a red tie bearing the Chaldea insignia, a black skirt, tights, and brown shoes. Her signature combat ensemble is skin-tight black and purple armor resembling a mini-dress with an exposed midsection, complemented by black gauntlets, boots, a thigh garter, and a large cross-shaped shield. Later, she utilizes the Ortinax armor, a technologically advanced suit featuring thigh-high boots and a visor, designed to enhance her physical capabilities when Galahad withdraws his cooperation. Personality-wise, Mash presents as kind-hearted and mysterious, carrying underlying sorrow due to her limited time. Raised in isolation, she exhibits naïveté and lacks worldly experience, though she possesses extensive academic knowledge downloaded from Chaldea's Sheba system. Early on, she resembled a "blank slate," devoid of envy or hatred, incapable of comparing herself to others. Encouraged by Romani Archaman, Chaldea's medical director, she developed individuality, forming personal opinions and aspirations. She consistently addresses others with honorifics like "senpai," particularly Ritsuka Fujimaru, viewing them as a reliable anchor. Her paramount loyalty manifests in prioritizing Ritsuka's safety during battle while concealing personal fears. Unspoken romantic feelings for Ritsuka surface as blushing or jealousy during interactions with others, though she remains unaware of their nature. She enjoys detective fiction, especially Sherlock Holmes stories, and often serves as the straight man to comedic antics from figures like Dr. Roman. Mash stands as the sole known Shielder-class Servant, wielding defensive abilities centered around her shield. Her initial Noble Phantasm, Lord Chaldeas, erects a protective barrier. During the Camelot Singularity, it evolved into Lord Camelot, amplifying party-wide defense and granting an attack buff. In combat, she functions as the primary tank, capable of blocking catastrophic assaults like Ars Almadel Salomonis, though this resulted in her death during the Final Singularity. Fou resurrected her using accumulated energy, extending her lifespan. Following this, Galahad ceased cooperation, rendering her unable to manifest Demi-Servant abilities until Ritsuka expended a Command Spell for temporary restoration. The Ortinax armor later compensated for Galahad's absence, integrating the Black Barrel Replica—a potent firearm deployed against deities like Aphrodite and Zeus. Her skills underwent multiple enhancements: Transient Wall of Snowflakes became Exalted Impervious Wall of Snowflakes, improving damage mitigation, while Ortinax abilities gained offensive traits like Ignore Defense effects. In the Babylonia Singularity, Mash supported Ritsuka defending Uruk against demonic beasts and the Three Goddess Alliance. She interacted with Servants like Leonidas I, who trained her in defensive tactics, and Ishtar, whose tsundere demeanor contrasted with Mash’s earnestness. Her resolve solidified here, reflecting her broader character arc: accepting life's hardships as meaningful despite their impermanence, a philosophy directly countering antagonists like Goetia who sought to eliminate suffering by erasing humanity. Post-Babylonia developments include her role in the Lostbelt saga, where she initially struggled with identity and purpose without Galahad. The Ortinax suit’s limitations left her vulnerable to high-level threats until she regained confidence through battles like those in the Anastasia Lostbelt. During Avalon le Fae, she fully reclaimed her abilities after resolving internal conflicts, ascending to a higher Saint Graph level. Her bond with Ritsuka remains central, symbolizing her commitment to preserving human history.