Gamba is a wise and naturally combative sewer rat dwelling in the city's underground systems alongside his community. His first appearance occurs when he becomes trapped on a street pile of chewing gum, narrowly avoiding an oncoming car thanks to Glikko, a chipmunk recently escaped from domestication. After this rescue, Gamba recruits Glikko to confront a troublesome gang of house rats. He explains that house rats damage human property, leading to sewer rats being falsely blamed. Gamba leads Glikko to the sewer rats' home, where hostile house rats surround them. In the ensuing battle, Gamba orchestrates a strategic victory by releasing stacked pipes and rolling a tire into whiskey barrels to defeat the attackers. He then celebrates triumphantly with the sewer rats and Glikko.

The next day, Gamba guides Glikko out of the sewers. When invited to accompany Glikko onward, he declines, asserting his place remains with the sewer rat community in the city. Gamba advises Glikko that the forest wilderness is the chipmunk's true home before they part ways. His role contrasts the antagonistic house rats through demonstrated loyalty to his group, tactical leadership in conflict, and a firm sense of belonging to his urban environment. His name, meaning "battler" in Japanese, reflects his combative nature and defensive role for his community.