Tatsuo Kusakabe serves as a university professor in archaeology, moving with his daughters to a rural house to stay near his hospitalized wife Yasuko, who suffers from a long-term illness tentatively identified as tuberculosis. His academic work demands substantial time at home, occasionally limiting direct daytime oversight of his younger daughter Mei.

He possesses dark hair and eyes, a tall slender frame, and wears thick black glasses. His typical clothing includes shirts with pullovers, or specifically a red vest layered over a white undershirt paired with blue trousers.

Patient, kind, and emotionally warm, he engages sincerely with his daughters' imaginative accounts of spirits like Totoro and soot sprites (susuwatari), never dismissing their experiences. He reassures them during moments of fear—reframing their "haunted house" as exciting and using laughter to help clear susuwatari from their home. He consistently maintains a calm demeanor, avoids harshness, and encourages finding joy through laughter even during storms.

Within his family, he demonstrates deep affection and support, managing household duties and childcare while Yasuko recovers to foster security for Satsuki and Mei. His interactions include playful activities like bath time and validating their perspectives on forest spirits. His relationship with Yasuko reflects mutual care and concern during hospital visits where they discuss family well-being. He also maintains respectful, friendly ties with neighbors such as Granny.

A subtle detail hints at a possible Hokkaido connection through a novelization scene where he sings a song associated with Hokkaido University. His character remains consistent throughout the narrative, providing steady emotional support without significant transformation, and he does not appear in the spin-off "Mei and the Kittenbus."