Sadi

Sadi is the chief guard of Impel Down. Her name comes from the word sadism.

Sadi resembles a dominatrix in design. She dresses in a very skimpy devil-themed outfit. She carries around a pitchfork and wears a headpiece that resembles horns. She has long hair that covers her eyes. She also wears candle-shaped earrings.

As her name suggests, Sadi is a sadistic person who enjoys bringing pain and torture to others, including Marine allies, and can't seem to get enough of their screams. She also seems to have extreme pride in the virtually perfect defenses of Impel Down, and refuses the assistance of the Marines.

She also tends to add an "mmmmm--!?" in the middle of her sentences, and insists to be addressed as "Sadi-chan".

Sadi is a chief guard of Impel Down with some authority over lower ranking subordinates. She appears to be in command over the Four Demon Guards.

The pitchfork she carries around conceals a custom-designed whip which she can use quite.

(Source: One Piece Wikia)