The Perfect Body
In order to don a Faust Robe, the user must have a female body. The male body does not have the necessary biological compatibility with a protector created and affixed through energy, thereby making the female form the most ideal. Cagliostro and Prelati formerly had male bodies, but after they embraced the wisdom and ideals of Saint Germain, she granted them the perfect body. In other words, she reconstructed them into super humans with a base female form. They also all share eternal youth granted by the power of Alchemy. The teachings of Alchemy have long led Alchemists to obtain "perfection" and this has now been found in multiple forms including "the Power of God," the "Lapis Philosophicus" and the "Perfect Body." Even without using the Faust Robe, their physical capabilities have enough power to match the Symphogear and the amount of life energy within them far surpasses that of a normal human. It was for this reason that Adam suggested that "the Perfect Body" be used as a sacrifice in order to make up for the lack of necessary energy to perform the ritual.