Kaonashi

Kaonashi is a translucent shape in a white mask, and it begins the film as very little: a lonely thing that follows Chihiro because she was polite to it once. It has no voice of its own. It offers her bath tokens, then gold, then more gold, and cannot work out why she keeps saying no thank you to all of it.

Inside the bathhouse it learns what everyone else there wants, and the staff teach it quickly. It swallows a worker, borrows his voice, and starts producing fake gold that the whole building queues for. Within an hour it is a bloated, roaring thing eating the people who are still bringing it food. Nothing made it that way except the room it was standing in.

Once Chihiro gets it outside it deflates back to the quiet shape it was, and it ends the film learning to spin thread at a cottage in the swamp. Miyazaki has described the greed here as a condition rather than a character flaw. The mask never changes expression through any of it.