Cagliostro and Prelati are trans btw. Saint Germain developed an alchemical technique early in her career to remake her body into a perfect one, making it immortal and an alchemical powerhouse. She offered that same technique to two male alchemists throughout her lifetime, which in turn gained female bodies and became her companions. They never really went over this in the show but it was stated in some supplementary material. Cagliostros jokes about her female intuition come from these events.
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