Matoi Giboshi serves as a police officer within the traffic enforcement division at Katsushika Police Headquarters. She belongs to the Giboshi family, owners of the Kanda district sushi restaurant "Chō Kanda Sushi," where she assists as a waitress and demonstrates knowledge of its dishes. As the daughter of the restaurant owner and granddaughter of Geparuto Giboshi (younger sister of Kanbei), she is a relative of Kankichi Ryotsu through their grandparents' sibling connection.

Physically, Matoi possesses dark brown hair styled in a high short ponytail with bangs framing her face, featuring longer locks on the left and right sides. She has brown eyes and eyebrows slightly thicker and arching higher than other female characters. Her recorded measurements are 85-59-84 cm, with a height of 173 cm and weight of 50 kg. Her birthday is April 30 and her blood type is O.

Matoi exhibits an energetic, tomboyish personality, distinguishing her from female colleagues. She is outspoken in her views, capable of a short temper comparable to Ryotsu's yet argues rationally. She holds deep knowledge of Japanese culture, surpassing Ryotsu, and actively supports traditional festivals in her hometown of Asakusa, Tokyo. Academically, she excelled as a pitcher on her high school's girls' softball team.

Her standard police uniform includes a white button-up shirt with a red tie and a dark blue or black skirt. Anime depictions frequently show her in a blue suit and skirt matching her Katsushika Police HQ colleagues.

She interacts professionally with colleagues Keiichi Nakagawa, Reiko Katherine Akimoto, Komachi Ono, and Naoko Seisho. Her familial relationships include her younger sister Lemon Giboshi and her newborn sister Mikan Giboshi. Family matriarch Geparuto Giboshi disapproves of Ryotsu and actively prevents Matoi and Lemon from developing romantic feelings towards him.