When she first appears in the second half of the film, she seems to be just as dangerous as her sister is. After wreaking havoc in Yubaba's office, she warns Chihiro (Sen) to keep quiet about the incident or she will rip her mouth out. When Chihiro refuses to hand over Haku and the golden seal, she becomes angry and yells at Chihiro, informing her that Haku is a greedy thief who needs to be punished, and that she placed a curse on the golden seal so that whoever steals it will die. She also appears to particularly dislike her nephew, Boh, shown when she makes fun of his weight and low intelligence.
When Chihiro visits her cottage in Swamp Bottom with No-Face, Boh and Yubaba's Bird in order to return the golden seal and apologize on Haku's behalf, her true nature is revealed as a kind and helpful old lady. She gives encouraging advice to Chihiro about remembering Haku's name, and later forgives Haku for the theft of her seal. She appears to form a bond with Chihiro, seen when Chihiro refers to Zeniba as "Granny" at her request.
Zeniba has the exact same appearance as her twin. She has an inhumanly-large head with long, white hair tied up into a bun. She has a wrinkled face, a hooked nose, a red dot in-between her eyes and wears blue eye-shadow. There are only one difference between the sisters, and that is Zeniba is shown to wear glasses, implying she may be far-sighted, as evidenced by the fact that she only wears them when weaving in her cottage. She also has large, golden earrings and wears a dark-blue dress decorated with rubies.
Zeniba first appears in the second half of the film. When Chihiro sees Haku in his dragon form being chased by the paper spirits conjured by Zeniba, she sees him crash into Yubaba's penthouse. Upon rushing there, one of the paper spirits follows Chihiro and attaches itself to her back. When she finally finds Haku in the office, being pushed down the chute by the Three Heads, she manages to stop them just as Boh crashes through the room in pursuit of Chihiro. When he begins to cry, Zeniba finally reveals herself when the paper spirit detaches itself from Sen and conjures up a transparent apparition of her. Taking delight in the circumstances, she wreaks havoc, transforming Boh into a small mouse, Yubaba's Bird into a tiny crow, and the Three Heads into a mimic of Boh's original form.
Zeniba lets Chihiro go as a thanks for leading her to a dying Haku, but threatens to rip her mouth out if she tells anyone about what she has witnessed. She demands Chihiro to move away so she can deal with Haku, but Chihiro refuses, stating that Haku is a good person. Zeniba then goes on to explain that Haku stole her powerful magic seal, and that he is a corrupt being who only became Yubaba's apprentice so he could steal her magic, and then goes on to state that Haku is dying because of a curse on the seal anyway. Whilst the Three Heads, now transformed into a Boh mimic, begin to bang around, Zeniba is annoyed and turns around to deal with them, giving an almost-dead Haku a chance to smash the paper spirit projecting her image, resulting in her apparition being sliced in half (apparently doing no actual harm to Zeniba herself).
Later on, despite warnings from Kamaji, Chihiro decides to take the seal back to Zeniba and apologize for Haku's actions. After taking the spirit train to Swamp Bottom, a magical hopping lantern leads Chihiro and her three followers (transformed Yu-Bird and Boh and No-Face) to Zeniba's cottage, where she greets them warmly. She subsequently invites them inside for tea. When Chihiro gives her the seal and says that she squashed a little black slug, Zeniba laughs and claims that she accidentally destroyed a parasite that was put into Haku by Yubaba to control him, and that her own curse from the golden seal was broken by Chihiro, whose love for Haku had proven to be more powerful. She gives Chihiro advice on remembering Haku's name so he can be free, and then compliments No-Face on his excellent weaving when she gathers everyone for a sewing session.
When it is time to leave, Chihiro thanks Zeniba for all she has done, and entrusts Zeniba with the secret of her true name. Zeniba remarks that it is a beautiful name, then turns to No-Face and offers for him to become her apprentice in weaving, to which No-Face happily accepts. When Haku arrives to take Chihiro back to The Bathhouse, Zeniba personally forgives him. She is last seen waving with No-Face to Chihiro, who waves back whilst riding on Haku into the sky.