Caster, recognized as the mythological Medea, serves as a Caster-class Servant within the series. Rooted in ancient Greek lore as a sorceress entwined with tragedy and formidable magical knowledge, she exists in an alternate reality bound to Souichirou Kuzuki, a teacher dwelling at Ryuudou Temple. Here, she strives to assimilate into ordinary life, methodically honing domestic abilities.

Her narrative pivots when she seeks culinary instruction from Shirou Emiya to prepare a dish for Kuzuki—a deliberate shift from her mythic role as a manipulative figure toward a caregiver. This endeavor reflects her resolve to comprehend human bonds through food, contrasting her legendary solitude. Her subdued, introspective demeanor emerges through quiet interactions, emphasizing her disciplined study of Japanese cuisine.

Distinctive traits like pointed ears, a choker, and gloves align with her mystical heritage. Though possessing teleportation and spellcasting skills, these are subdued in favor of routines focused on cooking and household harmony. Her steadfast bond with Kuzuki anchors her, with culinary efforts symbolizing a conscious departure from her mythic identity toward tranquil coexistence.