The Soot Sprites (すすワタリ, susuwatari, lit. "travelling soot", "soot sprites") are spirits that appear in the films My Neighbor Totoro and Spirited Away. They are small, round balls made from the soot that dwells in old and abandoned houses and leave black dirt in their wake. If the house becomes inhabited, they decide if the inhabitants are nice people. If they are, they will leave.
The Soot Sprites (conjured from soot itself) are small, black, fuzzy creatures with spherical bodies and white eyes with black pupils. Their usual mode of transportation is levitating/hovering, but it is revealed in the film that they can extend black, wiry limbs (arms and legs) from their bodies to accomplish certain tasks (in this case, moving coal into the furnace) and can lift objects many times their own weight. They also dissolve into soot if crushed, but quickly reform themselves shortly after.
My Neighbor Totoro
Sootballs appear at the beginning of the film when Satsuki, Mei, and Tatsuo Kusakabe first move into their new house. The Sootballs were noticed when they left around black dirt which is soot dust within the attic of the Kusakabe house which ended up on Mei's hands and the soles of both Satsuki and Mei's feet. They are everywhere and move quickly from the light into the shadow, which they take a liking to. Mei tries to catch some, but despite this, they agree that the Kusakabe family is good and they leave to another abandoned area. When one of them gets caught, they all become dust.
They work in the Bathhouse in return for small star-shaped food, called Konpeitō. They are seen carrying coal to help power the boiler in Kamajī's Boiler Room. The have super strength relative to their body weight. Even Chihiro Ogino couldn't take a piece of coal without overextending herself.
The Sootballs are friendly towards Chihiro. They are hopping when Chihiro leaves the Boiler Room. When Chihiro first meets Kamaji and gets rejected for a job, she helps the Sootballs carrying the coal. Soon, they lay down their coal at Chihiro's feet. Kamaji gets angry at Chihiro. Sootballs try to protect her by surrounding her. Kamaji explains that Sootballs absolutely should work, because if they don't work the spell which turns them in this creatures would break and they would return lifeless soot. After that, Lin comes Kamaji helps Chihiro by sending her to Yubaba. So Chihiro takes off her shoes and socks to walk better on the wooden floor of the Bathhouse, putting the removed socks inside the removed shoes, and the Sootballs intentionally carry them in their burrow to keep them safe.
Sootballs appear again when Chihiro returns in the Boiler Room for going outside, so they bring her back her shoes and socks. Chihiro thanks them, and then she puts on her shoes. Strangely she doesn't wear the socks again, taking them in her hands instead of wearing them.
When Chihiro changes clothes for working in the Bathhouse, Sootballs will also take care on other her clothes she wore outside, her striped shirt and her shorts.
Soot Sprites are not capable of speaking human languages and instead make certain, squeaky, murmuring sounds when they are excited, angry, annoyed or ecstatically happy. It is mentioned that, because the Soot Sprites in the film are magically conjured, they will turn back into soot without a job for them to do. While they are not capable of speaking the human language, they are shown to be able to understand it, and respond to orders given to them by Kamajī. They are also capable of exhibiting very human emotions, such as anger and happiness. They are also capable of showing affection to an individual, as seen when they begin to respect and support Chihiro in small ways after she is accepted by the workers of the bathhouse (mainly Kamajī and Lin). They carry Chihiro (or Sen)'s shoes and socks when she can't find them, showing that they care for Chihiro.
One can feed Soot Sprites like how a farmer feeds chickens, throwing handfuls of Kompeitō (a hard Japanese candy) from a bucket onto the ground for them to pick up and eat. The Susuwatari are not seen eating anything else other than kompeitō in the film.