Mii, also referred to as Mii-chan, is a minor supporting character in Haven't You Heard? I'm Sakamoto. She is a female high school student who belongs to Megumi Fujita's circle of friends. Her appearance is that of a bespectacled teenage girl with short brown hair cut in blunt bangs and red-framed glasses. She typically wears the standard school uniform, which includes a blazer, neckerchief, knee-high socks, and Mary Jane shoes.

As a background-classmate character, Mii has very limited on-screen presence and dialogue. Her role in the story is primarily that of an extra within the larger student body; she is occasionally seen accompanying Fujita and other female classmates during everyday school interactions. No distinct personality traits, personal motivations, or individual story arcs are depicted, and she does not undergo any noticeable development over the course of the series. She does not possess any special abilities or skills beyond being an ordinary student. Her key relationships are defined by her membership in Fujita's friend group, though the nature of their friendships is not explored in depth. Overall, Mii functions as a part of the school's social scenery rather than as an active participant in the narrative, and her character remains largely undeveloped.