Mei Yanase is a student at a女子高中 and serves as the class representative for her first-year class. With gray eyes and black, shoulder-length hair that she often wears in a side ponytail, her appearance is neat and orderly. Her birthday falls on July 22.

Yanase is characterized by a highly serious and earnest personality, taking her responsibilities and school life seriously. This seriousness is a defining trait, especially when contrasted with the odd and unconventional behavior of her teacher and many of her classmates. Upon starting high school, she found herself in a classroom described as full of strange people, an unexpected situation that she had not anticipated.

Her primary role in the story is that of the class representative, a position she was forced to take on during a chaotic first day, rather than one she volunteered for willingly. This role naturally places her in a position of authority and order within the otherwise relaxed and unusual daily lives of her peers.

A key relationship in her life is with her friend, Manaka, as Yanase is highly competitive with her. This competitive spirit motivates much of her actions and adds a layer of drive to her otherwise serious demeanor. Because of this, she is given the nickname Yananchou.

Her development is subtle, largely stemming from her adjustment to being surrounded by a very odd teacher and similarly odd classmates. Her journey is one of navigating her serious nature in an environment that rarely follows her expectations, forcing her to adapt to the upheaval and humor of her new high school life. There is no reliable information regarding notable abilities or a more detailed background.