Mash Kyrielight is a Demi-Servant, a human fused with the Heroic Spirit Galahad, leading to her classification as a Shielder-class Servant. Created via artificial fertilization and genetic editing under Chaldea's former director Marisbury Animusphere, she was designed as a vessel for Heroic Spirits. The project aimed to control Heroic Spirits by binding them to compatible hosts, though initial attempts saw Galahad refuse full awakening despite being bound to her. This refusal arose from Galahad's disapproval of Chaldea's methods, though he remained within Mash to ensure her survival after a failed escape attempt. Her creation granted her a fixed lifespan of eighteen years, a fact known to her and her physician Romani Archaman from an early age. By the start of her involvement with Chaldea's operations, approximately two years remained. Mash possesses lilac hair, lavender eyes, fair skin, and an athletic build often noted by others. Her Demi-Servant status maintains her physical appearance at its peak, preventing visible aging. In casual settings, she wears rectangular glasses, a grey hoodie, a black shirt layered over a white-collared shirt, a red tie bearing the Chaldea insignia, a black skirt, tights, and brown shoes. Her combat attire consists of skin-tight black and purple armor resembling a mini-dress with an exposed midsection, black gauntlets, boots, a thigh garter, and her signature cross-shaped shield. During periods of waning cooperation from Galahad, she utilizes the Ortinax—a technologically advanced armored suit with thigh-high boots and a visor—to enhance her physical capabilities. Raised initially in isolation, Mash exhibited a blank-slate personality devoid of personal desires or emotions, a deliberate design to facilitate Heroic Spirit fusion. Under Romani Archaman's guidance, she developed self-awareness and began forming her own identity. She is characterized as kind-hearted, earnest, and deeply loyal, particularly to her designated "senpai," Ritsuka Fujimaru, whom she views as a role model of perseverance and humanity. Despite naïveté regarding social norms due to limited life experience, she displays extensive academic knowledge, especially in history, gained through Chaldea's Sheba education system. She harbors a fondness for detective stories, particularly Sherlock Holmes, and demonstrates subtle romantic feelings toward Ritsuka, though she lacks the experience to recognize them. Her interactions often involve serving as the straight man in comedic or chaotic situations, particularly with Romani or Ritsuka. Mash's primary relationships center on her mentor-student bond with Romani, whom she trusts implicitly, and her partnership with Ritsuka. She refers to Ritsuka exclusively as "senpai," reflecting her admiration for their ordinary yet resilient humanity. This dynamic extends into spin-off media like *Fujimaru Ritsuka wa Wakaranai*, where her earnestness contrasts with Ritsuka's comedic misunderstandings, often leading her to chastise other Servants' antics or provide grounded commentary. She retains residual respect for her former instructor Lev Lainur Flauros, complicating her perception of his later antagonistic actions. Negative sentiments surface toward individuals like Beryl Gut, who tortured her, and Saber Lancelot, influenced by Galahad's unresolved grievances. Her story begins as a member of Chaldea's Team A, assigned to the "Spatial Singularity F" expedition. During the Chaldea explosion incident, she and Ritsuka Rayshift to Singularity F: Fuyuki, where her latent Demi-Servant abilities awaken. She contracts with Ritsuka and manifests her Noble Phantasm, Lord Chaldeas, to block an attack from Saber Alter. Throughout subsequent Singularities, she evolves from a reserved observer to a determined protector. In the Camelot Singularity, she learns Galahad's identity and upgrades her Noble Phantasm to Lord Camelot, gaining enhanced defensive capabilities and a party-wide attack buff. Her resolve solidifies during the climax against Goetia, where she sacrifices herself using Lord Camelot to shield Chaldea from Ars Almadel Salomonis. Fou resurrects her afterward, expending his accumulated energy to grant her a normal lifespan. Following this, Galahad withdraws his cooperation, rendering her unable to function as a Demi-Servant. During the Lostbelt arc, Ritsuka restores her abilities temporarily via Command Spell, though her powers remain unstable until Avalon le Fae, where she regains full control by reconciling her resolve. In these later chapters, she adopts the Ortinax suit and wields the Black Barrel Replica—a powerful firearm—to defeat entities like Aphrodite, Demeter, Zeus, and Cernunnos. Her Noble Phantasm further evolves into Lord Camelot (Ortenaus) during the Nahui Mictlān arc. Mash's combat abilities emphasize defense and team support. She utilizes her shield for physical protection and employs skills like Transient Wall of Snowflakes (later upgraded to Exalted Impervious Wall of Snowflakes) for party defense buffs and damage reduction. Her Noble Phantasms, Lord Chaldeas and Lord Camelot, provide massive defensive barriers; the latter reflects attacks in adaptations like *First Order*. In her Ortinax form, skills like Black Barrel Replica enable offensive actions with defense-piercing properties. She also possesses a passive ability called Stargazer's Journey, increasing bond points for the party during Lostbelt missions.