Kotomi Tsuda (in Japanese Tsuda Kotomi) is the younger sister of Takatoshi Tsuda, who she affectionately calls "Taka-nii". Like her brother, she ultimately ends up attending Ousai Private Academy because of its proximity to home. She is considerate and caring toward others, but is curious and extremely (Takatoshi would say embarrassingly) enthusiastic about adult matters.
During her initial appearances in the manga and throughout the first season of the anime, Kotomi was still in Junior High School. She later takes the entrance exam to Ousai Academy in Episode 12 of the anime and enters as a First Year student in the Season 1 OADs. It's hinted a big part of the reason she passed the entrance exam despite her admitted weakness in studying was because one of the teachers who interviewed her happened to be Naruko Yokoshima, who saw Kotomi as a kindred spirit.
Kotomi is a cute girl with long dark brown hair normally worn in twintails. She has big brown eyes and often has a big smile or grin on her face. She is more stylish than her brother, often wearing different outfits on her days off.
On a few occasions it has been observed that her breasts have grown quite a bit since entering high school, as she complained that her first uniform felt tight around her chest.
Kotomi is a bright and cheerful girl who makes friends easily. She is very popular among her classmates and has many friends, even among seniors like Mutsumi Mitsuba. She is naturally charming, to the point Suzu thought she could be an idol.
However, Kotomi is also rather lazy and unmotivated, resulting in her being rather book-dumb and needing a lot of coaching from Takatoshi or Suzu to even keep up with Ousai's standards. In addition, she has a vivid imagination and often acts childishly, such as pretending she is the main character in a shounen anime.
Worse still is her shameless interest in adult matters, especially the kinkier forms of sex. Like Shino or Aria, she is well versed in common tropes found in galge (the term for dating simulation games like Love Plus or Amagami) as well as pornography. She doesn't seem to have any sense of time or place, happily talking about sexual-related matters anywhere and with anyone, much to the chagrin of Takatoshi or her best friend Toki.
There have been jokes surrounding Kotomi and Takatoshi about incest. Her interest in perverted matters, her airheaded & easygoing nature, and her tendency for jokes and not taking things seriously all culminate in making it difficult to tell whether Kotomi is straight-up joking about feelings for Tsuda or if there really is something there that she doesn't tell anyone. There have been no strong indicators to show Kotomi having real incestuous feelings for her brother.
Kotomi's relationship with her older brother is very good. Having been close since early childhood, the two siblings have played together for many years and have been on good terms for the duration of their time with one another. Kotomi seems to heavily rely on her older brother given that their parents seem to be away on business trips a lot. She In the instances in the series where Kotomi is in serious dialogue, she displays an ingrown affection and trust for Tsuda befitting that of a loving younger sister.
Kotomi has joked around with the concept of incest multiple times throughout the series, but it's most plausible that a combination of her pervertedness and airheadedness has led to the jokes surrounding this. There are no real indications of Kotomi having any feelings towards her older brother as a man.
Kotomi, perhaps due to her easygoing and airheaded nature, doesn't find Tokki's somewhat agressive behavior and way of speaking intimidating at all. This eventually led to Kotomi discovering Tokki's true nature as a clumsy, tomboyish, and misunderstood girl. Kotomi clearly displays feelings of platonic love and great friendship for Tokki. The two are often seen together in many instances throughout the series, with Tokki filling in for the straight-man-role in Tsuda's absence.
Kotomi holds respect and trust for Shino but treats her as she would treat a normal friend despite those things. Her rarely displayed, perhaps better described as subtle, admiration for Shino and the other members of the Student Council have led to a very healthy friendship between her and Shino. It could be said that Kotomi relies too much on Shino's somewhat forgiving and tolerant nature, though this is also evident in her interactions with other people like Tsuda, Suzu, and Uomi.
Kotomi is comfortable enough with Shino to make plenty of jokes, a fact that is present throughout the entire series. It's also implied that Kotomi, being as surprisingly perceptive as she has been portrayed, is at least vaguely aware of Shino's affection for Tsuda.
Kotomi and Aria get along very well. She is also comfortable enough with Aria to make the same jokes as she would with Shino.
Kotomi holds great respect for Suzu as an upperclassman who is very capable and reliable. The two have a good relationship and are friendly with one another. Suzu plays the straight-man-role either in tandem with Tsuda or alone whenever Kotomi makes her jokes.
How much Kotomi has noticed with regard to Suzu's feelings about her brother is not as clear as it is with Shino. It can be assumed that she knows about Suzu's feelings on the matter.
Locations associated with Kotomi Tsuda
- Her breasts are now larger than Shino's, something that irritates Shino greatly.
- The "little sister who has a crush on her big brother" angle is a common theme among mangaka Ujiie Tozen's work. It is even the main theme of one of his previous works Imouto wa Shishunki (in Japanese 妹は思春期 literally meaning My Sister is in Puberty). Another character with an apparent crush on her older brother appears in his latest work Puchi Puchi Tantan Puchitantan (プチプチたんたん プチたんたん). Unlike Kotomi, however, these girls are dead serious about their interest in their older brothers. The sister in Imouto wa Shishunki often attempts to flirt with her brother (who ignores her) while the sister in Puchi etc. seems to act as though she and her brother are already married, even claiming he was her boyfriend (the brother laughs it off as her idea of a joke).
- In the third episode of the second season's OVA. At The Ousai Academy Student Council Rules section before the opening, it is shown the girls wearing wedding clothes where they are meant to be tsuda's brides such as Shino, Suzu, Aria, Mutsumi, Uomi, and Kaede. But the most surprising thing is that Kotomi is also there which makes Tsuda confused.
- The kanji for her name translates to "Harbor/Port" (津) and "Paddy Field" (田)