Mutsumi Mitsuba is the leader and founder of the school's judo club, as well as being the classmate of Takatoshi Tsuda and Kenji Yanagimoto. In the second year, she becomes classmates with Suzu Hagimura, Nene Todoroki and her best friend Chiri Nakazato as well. She is a very strong and highly skilled fighter, and very dedicated in leading her club. She also comes off as being innocent and naive (she is sometimes referred to as 'pure') compared to other girls in the series.
Mutsumi is a pretty girl with long black hair that reaches halfway down her back. In all her appearances, she wears it in a ponytail starting from the upper-back part of her head. She is in excellent shape and her best friend Chiri has noted she has nicely shaped breasts.
Mutsumi is a kind and energetic girl who makes friends easily among both boys and girls. She is known as a moodmaker (i.e. someone who can improve the mood of others just by being there) due to her cheerful and uplifting personality. She is also very innocent and pure-hearted, often misinterpreting the perverted comments of Aria Shichijō and Shino Amakusa. However, while she excels at sports and physical education, she is a poor student in other subjects. She has also admitted to dozing off in class and finds it hard to sit still for long periods of time.
Takatoshi Tsuda addressed as 'Takatoshi-kun'
Mutsumi is one of the only people in the series who addresses Takatoshi by his first name on a regular basis (the others being his sister Kotomi and relative Uomi). The two of them get along very well, as Takatoshi finds her refreshingly normal compared to the Student Council members. He also seems to find her innocence charming, and often tries to shield her from the perverted comments of girls like Shino, Aria and Ranko. He at the very least finds her attractive to boot.
For Mutsumi's part, she has nursed a crush on Takatoshi quite possibly since their first meeting, when she approached him for help in setting up the Judo Club. She apparently talks about him a lot with her friends, which leads to Chiri teasing him when they meet for the first time. Mutsumi also sometimes shows embarrassment when she looks bad in front of Takatoshi, such as the time she tried to avoid standing too close because she was still sweaty. In Chapter 249, she hurriedly fixes her hair and straightens her uniform when she realises Takatoshi just walked into the room. Some people (such as Ranko Hata) are aware that an easy way to get Mutsumi to agree to something is to get Takatoshi to ask her.
Overall, they have a very comfortable relationship, though the Judo Club (and a few others) suspect Mutsumi would definitely like said relationship to be deeper.
Chiri Nakazato addressed as 'Chiri'
Chiri is Mutsumi's best friend and Vice-Captain of the Judo Club, and the tsukkomi to Mutsumi's boke. They usually have lunch together and Chiri is one of the few people who can keep up with Mutsumi during training. She is also trying to help Mutsumi in relation to her crush on Takatoshi, but due to Mutsumi's own innocent personality she finds it difficult.
Nanako Umibe addressed as 'Nanako'
Nanako is one of Mutsumi's original members of the Judo Club as well as part of her circle of friends. She was one of the girls who pushed Mutsumi into approaching Takatoshi about forming the Judo Club.
Suzu Hagimura addressed as 'Suzu-chan'
Mutsumi and Suzu are good enough friends to call each other by first names (Suzu-chan and Mutsumi respectively). In addition, Suzu sometimes helps coach Mutsumi with her studies, and Mutsumi has gone on sleepovers at Suzu's house on at least two occasions.
Shino Amakusa addressed as 'Kaichou' (President)
Mutsumi looks up to and respects Shino due to her status as Student Council President. However, due to her innocence, Shino's perverted comments often go over her head or are misinterpreted as proper advice.
Aria Shichijou addressed as 'Shichijou-senpai'
Like Shino, Mutsumi looks up to Aria. Also like Shino, most of Aria's comments tend to be misinterpreted by Mutsumi. For example, Aria's comment that boys could satisfy her needs (sexually) was interpreted as 'being around boys will make you less hungry'.
- Mutsumi makes a very brief appearance in the first episode of the first anime, shortly after Takatoshi passes the ticket machines. She is seen running from right of the screen to the left. She is carrying a judo uniform with her.
- She suffers severely from motion sickness, even being on Takatoshi's shoulders made her feel ill. For this reason, she hates taking the bus when the Judo Club goes to practice matches and occasionally gets depressed over it.
- Mutsumi has at least once outright admitted to herself that Takatoshi is cute.
- While she is able to chat with Takatoshi easily, when it comes to physical contact she sometimes panics and freezes when she realises who she is touching.
- In Chapter 178, while she is unaware of it, Takatoshi was watching when Mutsumi was in her sweat-drenched p.e. uniform and blushed before looking away.
- In Chapter 255 of the manga, when Takatoshi offers her a hand to pull her up, Mutsumi decides to play a prank and pull on his arm to make him stumble (i.e. how someone might pull a friend into a swimming pool). She winds up pulling Takatoshi on top of herself, causing herself to freeze in a panic.
- While most often people point out that Takatoshi is oblivious to the feelings of the girls around him, Mutsumi is sometimes oblivious to chances to get closer to him. A recurring example is her athleticism allowing her to perform sports easily, while the other girls sometimes get help from Takatoshi (e.g. during an outing to a skating rink, Takatoshi spent some of his time holding hands with Shino, Aria and Suzu due to them not being used to skating, while Mutsumi literally danced circles around them. Chiri actually points out how clueless Mutsumi is, to which Mutsumi simply stares in confusion.
- The kanji for her name translate to "Three" (三) and "Leaf" (葉), which together refers to Japanese parsley or honewort