Little Chu (nicknamed Chewy) is a gray mouse sporting his grandfather's style of glasses, a white long-sleeved shirt, green pants, and a blue tie, with mitten-like hands fitting the show's aesthetic. He lives with his grandfather, Cube Town's top inventor Dr. Chu, within a gadget-filled research institute. This environment fuels his own inventive talent; he regularly aids Dr. Chu and crafts personal creations like solar-powered sunglasses, while also sharing his grandfather's passion for comic books.

Chewy balances caution with curiosity. As Pecola the penguin's closest friend, he often joins Pecola's schemes despite vocal reluctance and anxiety—frequently described as a "funny feeling" in his stomach—about potential trouble, making him an unwilling yet loyal accomplice. He possesses a competitive streak, challenging friends and even Dr. Chu. Though generally kind and sociable, he navigates interpersonal tensions, particularly stemming from his crush on Steamer the cat train engineer, which sometimes strains his friendships.

A key episode tested his relationship with Dr. Chu. Misinterpreting his grandfather's critique of his solar sunglasses (intended only for indoor use), Chewy resolved to improve them. Pecola inadvertently fueled a public perception of an invention rivalry. Chewy's upgraded sunglasses malfunctioned, launching him skyward, requiring Dr. Chu's rescue in the "Mad Mouse" airplane. This resolved the conflict, reaffirmed their bond, and highlighted Chewy's growing confidence and skill alongside his grandfather's support.

Within Cube Town, Chewy participates in community life: joining beach activities, expressing skepticism about Pecola's riskier ideas (like using canned tornadoes for kite-flying), and navigating local events, solidifying his role as a well-integrated, though often apprehensive, resident.