Nun (as Sister Agatha)
Keeper of the Skull Heart
Affiliation(s):The Trinity.
Religion:Trinitism.

Double is one of the eight original playable characters in Skullgirls. Her home stage is the Grand Cathedral, but Gehenna is also referred to her "domain" and is even implied to be an extension of herself. Despite her taking on a female form as a disguise and her combat stance being feminine, her gender is still listed as Unknown on the official site which may be because she's not actually human.