Chipmunk, known as Shimarisu in the original Japanese, is one of the primary animal friends of the main character Bonobono and is a central figure in the series' gentle woodland setting. As a small, timid rodent, Chipmunk often embodies the anxieties and cautiousness that contrast with the more carefree nature of his companions. His most notable characteristic is his skittish and fearful demeanor. In many social situations, particularly when confronted by stronger personalities, Chipmunk’s immediate response is to assume he is about to be mistreated, frequently asking others if they intend to bully him. This defensiveness shapes many of his interactions and establishes him as the most vulnerable member of the main trio.

The background of Chipmunk provides context for his nervous personality. He comes from a very large family and has an absurd number of sisters, which has significantly influenced his behavior. Specifically, he has overbearing older sisters who frequently bully him at home. This dynamic has left him feeling oppressed and fed up with their unreasonable behavior, leading to occasional rebellious moments where he stands up for himself, such as challenging one of his sisters to a duel to stop her from pushing him around. His development often involves small but significant lessons about self-worth. Through his adventures, he learns concepts such as the value of not always having to be first, discovering that it is perfectly acceptable to be second best at something. Underneath his generally timid exterior, there are hints of a more complex personality, including a gleeful but usually hidden mean streak that surfaces on rare occasions. This suggests that his vulnerability is not his only trait, but a learned response to his environment.

Within the story, Chipmunk plays the role of the easily worried and cautious friend to the more optimistic and daydreaming Bonobono and the irritable and pragmatic Raccoon. This trio dynamic is the heart of the series, with Chipmunk often caught in the middle of Bonobono's strange logic and Raccoon's short temper. Raccoon frequently bullies Chipmunk, using swift kicks to punish the two friends for their foolishness, making Chipmunk the primary target of physical gags and highlighting his low status in the group hierarchy. Despite this, the three remain consistent companions who explore the forest, play games, and attempt to solve mysteries together. Chipmunk's key relationships are defined by these opposing forces: he is a nervous foil to Bonobono's obliviousness and a frequent victim of Raccoon's aggression, yet he is an essential part of their shared life.

Regarding notable abilities, Chipmunk does not possess superhuman powers but has typical animal behaviors adapted to his world. He is shown gathering walnuts in the north woods, demonstrating his instincts as a forager. He also participates in games of nerve, testing his bravery by sticking his hand into holes and confronting whatever crawls out, showing a capacity to face his fears even when his natural inclination is to be cautious. His most defining ability is his verbal expression of anxiety, using his catchphrase to question the intentions of others, which serves as a consistent source of humor and characterization. Through his daily life, Chipmunk provides a window into themes of fear, family, and finding small moments of courage in a quiet and often surreal forest world.