Sella, a homunculus crafted by the Einzbern family through alchemy, was initially designed for their Holy Grail experiments before being reassigned as caretaker and magic tutor for Illyasviel von Einzbern. Though she appears youthful, her existence spans roughly two years, sporting the Einzbern homunculi’s signature long, pale hair and typically clad in casual attire or her classic maid uniform.

In *Fate/kaleid liner PRISMA☆ILLYA*’s alternate universe, she acts as a guardian for Illya and Shirou Emiya during their parents’ absence, managing household affairs—cooking, cleaning, and nurturing the castle’s courtyard garden, which she tends meticulously, driven by devotion to Illya. Disciplined and strict, she rigorously upholds propriety and responsibility, especially toward Shirou as the household’s eldest son. She maintains a tsundere dynamic, openly chiding Shirou’s domestic efforts yet privately cherishing structure and etiquette.

Her rapport with fellow homunculus Leysritt is defined by contrast: where Leysritt embodies lethargy, Sella remains meticulous yet occasionally insecure, particularly about her physical appearance. This insecurity surfaces as sensitivity regarding her slender frame contrasted against Leysritt’s more curvaceous form—a trait leveraged for humor. Despite her stern demeanor, she reveals a gentler affinity for flora and fauna, favoring their companionship above most people.

Within the *Unlimited Blade Works* anime adaptation, she vehemently opposes alliances with outsiders like Rin Tohsaka and Shirou, prioritizing Illya’s safety above all. Confronting Gilgamesh, she showcases unyielding loyalty, defying retreat even when fatally injured—a testament to her protective nature, willing to relinquish her humanity to shield Illya.

Across media, her capabilities span expertise in household management, foundational combat techniques, and magecraft, though her frail homunculus physiology curtails her combat efficacy. She holds a driver’s license and practical competencies such as nursing, aligning with her caretaker role. Her characterization remains steadfast, emphasizing dutiful dedication and underlying vulnerability, particularly in comedic or slice-of-life contexts where insecurities or clashes with Shirou arise.

Spin-offs like *Carnival Phantasm* feature her in brief comedic vignettes, such as dragging Leysritt home or engaging with other characters, upholding her no-nonsense poise. The *Fate/kaleid* timeline highlights her relentless efforts to preserve normalcy for Illya amid supernatural chaos, oblivious to Illya’s magical girl escapades. Her origins as a repurposed homunculus and layered emotional landscape—juggling duty, insecurity, and concealed tenderness—anchor her character’s essence across all narratives.