Retz is a traveling puppeteer, an original character for the movie Phantom Rouge.
Retz is a female. Her gender was confirmed after Killua pushed her in the chest. She dresses like a a boy to hide her gender.
She is the younger sister of Omokage. She can control puppets without strings. Retz's eyes are not her own, but Omokage's. Retz is just a puppet created by Omokage in the image and mind of his little sister.