|Medical ☆ Medea|
The Caster (キャスター, Kyasutā?) Class Card of the Fourth Ainsworth Holy Grail War, and the Fifth Ainsworth Holy Grail War was granted to Ainsworth Doll, Atrum Galliasta. It was later one of eight Class Cards transported to Illya's world in Fate/kaleid liner PRISMA☆ILLYA.
When she manifested, Medea's appearance is slightly altered. Her cloak and dress have a tattered appearance, and white fur is draped across the shoulders.
Illya, Miyu Edelfelt, Rin, and Luvia encounter the manifested Caster under the Fuyuki Bridge. They are forced to retreat from her assault the first time, but later manage to beat her after Illya and Miyu learn to fly. Miyu kills her and retrieves the card by using Gae Bolg.
Illya later installs it to battle Beatrice Flowerchild, but she loses in a clash with Mjölnir. Illya then later includes it to utilize Rule Breaker on Julian Ainsworth, removing the conceptual duplicate of his ancestor from him. He then steals the card with Flash Air and destroys it in retaliation.
Medea is a "magical energy specialization type" able to utilize High-Speed Divine Words, lost magecraft from the Age of Gods, that allows her to activate spells too complex for modern systems of magic. She can unleash a great bombardment of magical energy from high-caliber magic circles, exceeding the bounds of magecraft, and it possesses destructive power that easily surpasses that of an average Noble Phantasm. In contrast, her physical ability is poor, and she said to be like "paper armor" in terms of defense. She possesses Rule Breaker, the "ultimate anti-magecraft weapon", that embodies her role as the Witch of Betrayal. Possessing no killing ability, it is able to break anything constructed from magecraft and return it to its former state.
- PRISMA material/petit - User of the Caster Card