Haku is a Yubaba's Apprentice, and second-in-command at the Bathhouse. He looks to be in his teens, and has a lean build. He has dark hair in a bob haircut, sharp grey-green eyes, and thin eyebrows. He wears a white kimono with blue trousers, along with a purple sash around his waist. As a River Spirit, he has the ability to transform into a dragon; an animal commonly associated with rivers and water in Japanese culture and mythology.
His dragon form is that of a typical Eastern dragon, with a long snakelike body, horns, flowing whiskers, and a lupine face. In this form, he is primarily white with a turquoise mane. He can fly, and he seems to have the ability to interchange between human and dragon forms at will.
- In the Japanese version of the film, Yubaba tells Chihiro that the price of failure in her challenge will lead to Chihiro having to kill and tear Haku to pieces herself. In the English adaptation Yubaba instead tells Chihiro that failure will lead to eternal imprisonment in the bathhouse.
- The name Haku means "master, lord, overseer", which may refer to his lofty position as Yubaba's respected apprentice as well as his power as 'god' of the river.