Banba is one of the residents of Amamizukan, the all-female apartment building in Tokyo that serves as the central setting for the story. She is a dedicated train otaku, possessing an encyclopedic knowledge of railway systems, train models, schedules, and the specific lines serving various locations, often volunteering this information unprompted in conversation. Her appearance is distinctive and unconventional, marked by a large, rounded afro hairstyle that becomes one of her most recognizable features. Among the residents, she is one of the smallest in stature, and she claims to be only eight years old, a playful reference to her being born on February 29th, a leap day, meaning she only celebrates a birthday every four years.

Banba has a blunt and somewhat boyish personality, often using the masculine pronoun ore when referring to herself, which can lead to viewer confusion regarding her gender. She is direct in her speech and her desires, and what she desires most is meat. She has an intense and singular passion for high-quality beef, particularly Matsusaka beef, which she considers a luxury. This craving is so central to her character that she frequently pesters the wealthy cross-dressing character Kuranosuke for meat, giving him the nickname Meat. Her love for meat extends to a peculiar and notable ability called the Meat Scope, a form of stat-o-vision that allows her to instantly judge the quality and marbling of meat, even from its packaging. She is deeply offended by any culinary faux pas that disrespects meat, such as placing shiratake noodles next to it.

Within the close-knit community of Amamizukan, Banba is part of a comedic duo with her fellow resident Mayaya, who is obsessed with the Romance of the Three Kingdoms. The two are often seen together, with their shared eccentricities and enthusiastic reactions to their respective hobbies forming a running gag throughout the series. Like the other residents, she is deeply averse to stylish people and social situations, but her primary role is as a source of comic relief, her obsessive personality and signature requests for meat providing consistent humor. While her personal development is not the primary focus of the overarching plot, which centers on Tsukimi and Kuranosuke, her distinctive traits firmly establish the quirky and insular world of the Amars.