Mari Tamaki is a self-aware yet unmotivated individual who often feels trapped in a repetitive daily routine. While she longs to make the most of her youth and experience something extraordinary, she struggles with hesitation and fear of stepping out of her comfort zone. This internal conflict is reflected in her behavior though she occasionally shows bursts of enthusiasm and determination, she frequently backs down due to anxiety about failure or change. Even something as minor as skipping school can leave her feeling nervous.

Her passivity is also evident in her personal habits, such as leaving her room messy without much concern. At the same time, Mari can become so focused on subjects that interest her like the idea of an Antarctic expedition that she forgets her surroundings, such as when she began reading aloud during class.

Despite her fears, Mari is loyal and kind-hearted. She shows strong moral character, choosing to return an envelope containing one million yen rather than keep it. Her loyalty is further demonstrated when she defends Shirase Kobuchizawa from bullies and remains by her side throughout the journey to Antarctica, even in the face of gossip and judgment. Mari also maintains her bond with her childhood friend Megumi Takahashi, inviting her to spend time with the new group.

As the series progresses, Mari becomes more determined and focused, taking on a part-time job to contribute to the cost of the trip. She is also known for her goofy and lighthearted side, often bringing laughter to the group with her antics like accidentally getting a reverse raccoon tan in Antarctica. While cheerful, she harbors a slight fear of her mother, who can be strict and intimidating, especially when Mari keeps secrets, such as her travel plans.

Mari is a teenage girl with neck-length light brown hair styled in a bob cut and hazelnut-colored eyes. Her features give her a bright and youthful look, and she is highly expressive, often seen making a wide range of animated facial expressions. Among her group of friends, she is the second tallest and has a slender, petite frame.

Her usual outfit is her school uniform, which includes a blue blazer, a red bow tie, a gray pleated skirt, black socks that rise above her shins, and pink-and-white sneakers. Outside of school, Mari wears various casual clothes, including a notable ensemble featuring a red shirt and pants, paired with a blue jacket.

She is known to be a restless sleeper. In several episodes, Mari is shown sprawled across the bed she shares with others, often causing frustration among her companions due to her tendency to hog space while sleeping.

Mari’s given name (マリ) is written in katakana, which typically carries no inherent meaning. However, if rendered in kanji, it could be interpreted in several ways, 真理 – meaning “truth” or “verity, 真里 – combining 真 (ma, “real” or “genuine”) and 里 (ri, “village”).

Her surname Tamaki (玉木) is composed of the kanji 玉 (tama), which can mean “ball,” “jewel,” “bead,” or “pretty girl,” and 木 (ki), meaning “tree” or “wood.”