Mai Minakami is a high school student known for her quiet demeanor and high intelligence, often appearing as the most reserved member of her friend group. She has long, straight ashy-black hair that reaches the middle of her back and expressive dark eyes, which are complemented by the glasses she always wears. Before the events of the series, Mai lived in Alaska due to her father's job before her family moved back to Japan, a transition that likely contributed to her initial difficulties in social situations. As a transfer student during middle school, she struggled with shyness to the point of privately practicing how to address her classmate Yuuko Aioi just to avoid an awkward encounter.

Mai is characterized by her almost perpetual expressionless face, rarely showing visible signs of emotion such as smiles, anger, or regret. This stoic exterior makes it difficult for others to discern what she is thinking, but beneath this calm surface lies a deeply eccentric and mischievous personality. Her defining trait is a love for elaborate pranks and deadpan humor, often executed with such precision and randomness that her friends are left confused or exasperated. She frequently targets Yuuko with her antics, ranging from wordplay and sarcastic retorts to complex practical jokes. Examples include deliberately placing her glasses on top of a precarious card tower Yuuko and Mio had built, staring at her friends for an unnaturally long time during a game of "Red light, green light," and even feigning romantic interest in Yuuko just to provoke a flustered reaction. Mai seems to have few limits when it comes to her jokes, sometimes engaging in pranks that border on bullying, yet she deliberately avoids involving children like the young genius Hakase in her schemes, suggesting an underlying sense of restraint.

Despite her antagonistic behavior toward her friends, Mai genuinely cares for them. She has been friends with Yuuko since middle school, and although she constantly undermines Yuuko's jokes, she chose to attend Tokisadame High School with her instead of a more prestigious academy. A brief flashback reveals that behind her deadpan exterior hides a shy and sensitive side, as she once lay in her room practicing Yuuko's nickname alone, only to hide her head under a pillow in embarrassment afterward. In rare moments of vulnerability, she has smiled warmly after witnessing a reconciliation between Yuuko and Mio or shown genuine surprise and joy while engaging in playful activities. Her perceptiveness extends to her friendship with the android Nano Shinonome, as Mai deduces Nano's robotic nature but keeps the secret without judgment, even returning a fallen screw to her home.

Mai possesses an impressive range of abilities that extend far beyond academics. She is a multi-talented individual who excels at fishing, wood carving, arm wrestling, handling projectiles, and even modeling. Her wood carving hobby frequently produces intricate statues of Maitreya Buddha, which she sometimes brings to school. She also writes and performs music, demonstrating a hidden artistic depth. Her physical strength is notable, easily defeating others in arm wrestling contests. Academically, she is an honor student who performs well on exams, yet she approaches her studies with an unusual nonchalance. Her intellectual curiosity may be reflected in a psychology book she has been seen reading, hinting at an interest in human behavior that could inform her pranking skills. At home, she enjoys playing video games and has several pets, including two dogs named Oguri Cap and Pyon and a cat named Chitchi. In later chapters, a time skip shows Mai has become a preschool teacher, indicating a significant but natural evolution from the quiet, prank-playing student into a caring educator.