(Part 45 of police waifus. Kochikame again. My favorite character in the series and one of my role models when growing up, so bio will be longer.)

(First opening is for female users, second is for males.)

Age: 20

Height: 173cm

Weight: 50kg

Body/Waist/Hips: 85-59-84

Birthday: April 30

Occupation: Policewoman for Tokyo Metropolitan Police Department's Shin-Katsushika Police Station. She is part of the traffic unit. Rank is Policewoman.

She is Ryotsu's second cousin, (they didn't know that when they first met) and because Ryotsu's younger brother Kinjiro married someone from Keiichi's famly, this makes her a distant relative of Keiichi as well. Her family runs a sushi restaurant called "Super Kanda Sushi" in Kanda, and she has an older brother named Yuutsu and two younger sisters named Lemon and Mikan. According to the author, she was introduced as a rival character who could compete and deal with Ryotsu.

A daughter of the promient Giboshi family, Matoi graduated from the prestigious Sakurarin University High School. Although she had passed the university entrance exam, she wasn't ready to attend college. After her high school graduation ceremony while participating in the Shirasen Nagashi ritual at Hijiribashi Bridge, she jumped into the river to save a child who had fallen from the train platform at Ochanomizu Station and rescued the kid. Matoi was surprised that the grateful mother and onlookers thanked her, and realizing that she enjoyed helping people, she decided to join the police force. The next day she submitted her application to a koban, passed the exam the following week, and entered the police academy. She received a letter of appreciation from the police for saving the child and was invited to join their station, but she was assigned to Katsushika Police Station after graduation. She often drops by at Kameari koban.

Due to her family's sushi-making background, she goes to bed at midnight and wakes up at 4am, and was always the first to arrive at school during her student days. She doesn't wear makeup and only uses normal shampoo to wash her hair. As a result, she gets ready faster than others. She always wears her uniform with sneakers, and no jacket even during the winter season. Despite being part of a considerable wealth, she prefers living a simple life, never looking down on others, just like Reiko and Keiichi.

She refers to herself as "watashi" (a feminine way of saying "I"). She has a strong-willed, tomboyish personality and speaks in a masculine manner (although she spoke in a more feminine manner in her early appearances). She generally speaks informally to everyone, even her superiors such as the police chief, which exasperates Ryotsu, and her grandmother Geparuto has also warned her to correct her speech. However, she uses polite language when speaking with Kennosuke, Haya's father. She consulted Haya about this, and Haya recommended playing koto and tea ceremony to calm her mind. With the 1 million yen bonus she received for winning the safe driving competition, she bought tea ceremony equipment and a koto, much to Ryotsu's astonishment. Her koto skills are slowly improving, but Ryotsu often tells her that she "lacks femininity" and that "her swimsuit isn't sexy."

Compared to Ryotsu, her grandmother Geparuto, and Lemon, she is more sensible, but she is also extremely ignorant of things she is not interested in or things that are too familiar to her, and sometimes makes crude remarks and acts in ways that are far removed from the norm compared to ordinary people. For example she once called Asakusa 'the countryside' because she rode on top of a portable shrine during a festival. She is also unfamiliar with the latest information technology and science, and did not even know what Google or LEDs were. For this reason, she used her grandma's old cell phone, but when the service for that model ended, she and Ryotsu considered buying a new one, and as a result, she has been permanently borrowing Ryotsu's iPhone often.

With her appearance, Ryotsu has also started to take on more of a straight-man role. Her relationship with Ryotsu even progressed to the point of almost getting married. Even though Grandma Geparuto was opposed to the marriage, (she never liked Ryotsu) Matoi fell in love with Ryotsu's good qualities (such as when Ryotsu punched an angry driver to protect Matoi when the driver insulted Matoi and when he made the usually surly Lemon happy). Ryotsu was also interested in marriage but also questioning himself whether he was more interested in money than marriage (plus fantasizing about running a sushi restaurant with her), and just before the wedding, he changed from calling her by her last name to calling her "Matoi," showing that they were both serious about each other. Grandma Geparuto, however was strongly opposed the marriage when she found out that Ryotsu, who had been using a false name, was actually related to them by blood (Geparuto and Ryotsu's grandfather are siblings... and yes, Geparuto is THAT old.) and Ryotsu's parents (Matoi's cousins and aunts) were also confused by the possibility of consanguineous marriage but Matoi still tried to marry Ryotsu despite Geparuto's objections, which resulted in Geparuto to reluctancly relent. Hilariously however, Matoi herself broke off the marriage a few minutes later when she witnessed Ryotsu's miserly nature, blinded by the wealth of the Giboshi family. (He sneaked inside the Giboshi family vault and left there for a few hours as a punishment. Ryotsu later fixed things with Giboshi family. He and Matoi decided to remain friends instead.)

Osamu Akimoto: "If Ryotsu and Matoi actually got married, the entire 'Kochikame' story would have an ending. So I revealed that they were second cousins, making them family members to end this amicably and continue the story."

Her best friend in the story is her fellow policewoman Reiko who often makes harsh remarks about Ryotsu, calling him things like 'a born con artist', 'a swindler', and often warns Matoi that if she does what Ryotsu says, they will both go bankrupt. They often hang out together and one time Matoi even gave her a clumsily hand-knitted scarf for her birthday, so they remain quite close. Reiko also occasionally asks her to keep an eye on Ryotsu when Ohara or Reiko isn't around. Matoi is also have a friendly rivalry with Haya, who is also her partner during patrols.

She is skilled at spinning tops, menko cards, and shogi, beating Ryotsu easily. In her childhood, she played baseball and softball and can throw a fastball that exceeds 150 km/h. Although her naginata skills are self-taught, having only been taught by Geparuto, she is skilled enough to fight Haya for over two hours without a clear winner. She is also a skilled driver, and together with Haya, she represented the Metropolitan Police Department in a safe driving competition for patrol cars and mini-patrol cars, and won the national championship. She is also a very good singer, having studied folk songs in her childhood, but she doesn't like to sing karaoke because she finds her mature singing style embarrassing. She also larned traditional Japanese dance from her mother from a young age.

Only thing she seems to be bad at is drawing. When asked to draw a coffee cup, she drew the front and top from the same angle, which was so bad that Ryotsu mocked her, saying it was "like a child's drawing." A manga drawn by Matoi was also harshly criticized Ryotsu, saying it was "worse than Lemon's." She has a low tolerance for alcohol and gets drunk after just one cup of sake. She used to wrestle with her brother, Yuutsu, and once, while drunk, she put Ryotsu in a neck lock and knocked him unconscious.