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The catbus is a forest spirit that acts as a omnibus for all of the other forest spirits, including Totoro. It first appears escorting Totoro on a rainy day. It also appears one day when Mei gets lost and brings Satsuki back to her sister, afterwards bringing them both to the hospital to give Yasuko Mei's corn.

The catbus drives Totoro around.

The catbus is a forest spirit like Totoro, and it also has a bit of Forest Magic. It can run faster than the wind and make the trees bend away so that it can get through. Ordinary creatures cannot see it, but animals such as dogs can smell it and may start barking. The catbus has twelve legs total and is light brownish orange with stripes of darker brown. It has four headlights in the form of mice and its eyes emit two rays of light, shining into the darkness ahead of it. It can only speak cat, but it seems to understand other languages as well. It is a compassionate creature and is always willing to help, though it prefers to stay invisible among older people.

The catbus helps Satsuki find Mei.