Būtarō Tomita, often referred to by his nickname "Boo-taro," is a classmate of the protagonist in the third grade of an elementary school. His distinctive nickname derives from his most recognizable feature: a pig-like nose and a verbal tic where he frequently ends his sentences with a snorting "boo" sound. This animal motif is further emphasized by the spirals drawn on his cheeks, which enhance his unique and memorable appearance.

In terms of personality, Būtarō is known for being a consistent and reliable presence within the classroom ensemble, contributing primarily to group dynamics and comedic situations rather than driving individual storylines. He is a supportive friend, sharing a particularly close bond with another classmate, Noritaka "Hamaji" Hamazaki, and the two are often seen together. He is also a regular member of the wider social circle that includes the main character, joining in various activities and adventures with the group. His motivations appear to center on maintaining these friendships and participating in the simple, everyday events of school life.

Within his own family, Būtarō lives with his parents and a younger sister named Tomiko. He shows a notable fondness and protective affection for Tomiko, demonstrating a caring and responsible side to his character as an older brother. He also has specific preferences when it comes to food, with his favorite items being pork buns and sea urchin.

Būtarō does not typically undergo significant personal development or serve as the focus of major character arcs. Instead, his role remains consistent across the long-running television series and related films, providing a stable and familiar part of the classmate ensemble. His primary ability, aside from being a loyal friend, is his recognizable speech pattern and visual design, which reliably contribute to the comedic and lighthearted tone of the series. He has no notable special skills beyond those of a normal elementary school student.