The spirit known as No-Face in Spirited Away is called No-Face.
No-Face is the English name commonly used for the quiet, masked spirit who enters the bathhouse where Chihiro works. In Japanese, the character is called Kaonashi, meaning “faceless.” No-Face initially appears lonely and harmless, but after being admitted into the bathhouse, it begins consuming spirits and producing gold, attracting the attention of the workers.
The character’s behavior changes dramatically depending on the environment. The bathhouse’s greed and constant desire for gold seem to amplify No-Face’s appetite and aggression. Later, after Chihiro gives it a cleansing herbal dumpling and takes it away from the bathhouse, No-Face becomes calmer and finds a more peaceful role with Zeniba.
The other choices are separate characters. Kamaji is the many-armed boiler-room worker, Haku is the river spirit who assists Chihiro, and Boh is Yubaba’s oversized baby. No-Face is not a personal name in the usual sense, but it is the canonical English character name and the fair answer to this question.