Zabimaru's spirit takes the form of a two people

an adult woman and a small boy, attached to the female's waist by a black chain that is connected to a collar on his neck. The female has dark green fur that covers most of her body, except for her inner abdomen and chest. She has green eyes, long, rose-colored hair (of similar color as the fur cowl that appears around Renji's shoulders in Bankai) that goes past her knees, and black markings in her hair that bear a resemblance to Renji's tattoos.

(Source: Bleach Wikia)