Tata is the steady older brother in a family of three black rats with brown fur, residing historically in a riverside tree trunk near Tokyo. His family includes only his father and younger brother, Chichi, after their mother's death following Chichi's birth. When human construction destroys their home, Tata supports his impulsive brother during the perilous family journey upstream before winter. He contributes to survival strategies as the group navigates natural and urban landscapes, facing threats and forming alliances.

Key allies include the Golden Retriever Tammy, who rescues Chichi from the river; the solitary brown rat Glen, who aids their escape from territorial conflict; and the Russian Blue cat Blue, who assists after a near-drowning. These encounters significantly shape the family's travel experiences and survival efforts.

In a subsequent mission, Tata and Chichi venture into the city to rescue their canine ally, Tammy, from kidnappers, demonstrating Tata's protective role extending beyond his immediate family.