Tatsuo is a professor working in archaeology at a university in Tokyo. He moves in an old, abandoned house in the idyllic countryside with his two daughters. His wife is at the hospital as a result of a long term illness (according to the timeline, something caused by radiation and likely to be cancer or TB.)
Tatsuo hears from his youngest daughter, Mei, about a giant spirit named Totoro. It is not clear whether he really believes her, but nevertheless does not doubt his daughter's honesty and tells her that Totoro is the "keeper of the forest" and encourages her train of thought.
A few nights later, Tatsuo is doing paperwork, when he hears his daughters screaming in happiness. It seems that he is assuming that they are with Totoro.
The hospital staff postpone his wife's visit, due to a setback in her treatment. Mei tries to run to the hospital and loses her way, which results in Tatsuo, his eldest daughter Satsuki, and some neighbors to search for her. Tatsuo visits his wife at the hospital, where they find an ear of corn that the girls left there.
Tatsuo does not appear in the ending credits.