" Tomorrow, I will get to see Oka, for the first time, wearing her school swimsuit during girl's PE swim class . . . . "
Of the four teenagers that are friends of one another, Ueno is the tallest of them, being a little taller than Tsubaki. His body build is somewhat thin and muscular, however, he is not especially athletic. He is of average weight for a slender teenage male. Ueno has short chocolate brown hair, worn in a mop cut, and chocolate brown eyes. His skin tone is a slightly dark, tan shade, with an even blend. He has an angular face, with a mildly chiseled jawline. He is always seen wearing glasses.
Aside from wearing the male school uniform to school, Ueno always wears casual outfits, mostly pants and shirts. His fashion sense is bland at best, making him one who never stands out in a crowd. However, when he is with Oka, his girlfriend, who is very short, they do make an interesting couple because of the noticeable difference in their heights. That, and the fact he dresses so commonplace, whereas Oka dresses somewhat provocative, sexy, and alluring out in public, they are quite a contrast in fashion styles.
Kouhei Ueno is Akria Tsubaki 's friend and Ayuko Oka's boyfriend. When Tsubaki first walked in on him and Oka kissing in an empty classroom at school, Ueno asked him to keep their relationship a secret, as Ueno is rather apprehensive about it. He magnanimously helps Tsubaki by providing advice about romantic relationships, and sometimes bragging about his relationship with Oka, unaware that Tsubaki is already in a relationship with Urabe. But when he finally finds out that Tsubaki and Urabe are shipping together, he seems to approve, because he realizes that Oka and himself are more advanced in their relationship than Urabe and Tsubaki.
Ueno has an overall mild personality, but has a definite, noticeable jealousy streak, especially with regard to Oka. Ueno is shown to be very jealous of Oka, and doesn't like the idea of taking her to the beach, since she prefers to wear a very sexy, reveling cream-colored bikini swimsuit. When on dates together, or when she is with Urabe, Oka also likes to dress in casual clothes that are a bit too daring and provocative for Ueno, subsequently, he also tries to keep some of his sanity by suggesting that she dress in more conservative styles, in order to avoid other boys from supposedly flirting with her.
Ueno does acceptable academic work at school, but his heart is not really into learning and education. More suited to being a 'party animal' and a fun sort of guy, Ueno spends a good deal of time on his favorite activities and hobbies, one being video games, instead of school homework. Many times Oka sees the need to tutor him so that he does not fall behind in school work, or start to fail his classes. However, Ueno sees the tutoring sessions as a chance to try and 'make out' with Oka, instead of doing any real studying.
Although Oka has the abilities to form a drool bond, and already has a romantic girlfriend/boyfriend relationship with Ueno, they do not have, and can never form, a drool routine between them, as Ueno does not have the ability to send, receive, or process drool. Because of this, or in spite of this, Ueno falls deeply in love with Oka, and highly values his relationship with her. Although not drool bonded to one another, like Tsubaki and Urabe are, or like Seo and Hayakawa are, nevertheless, Ueno and Oka have their own special bond that they enjoy with one another. They have a fun, quirky, somewhat playful and erotic S & M relationship that they enjoy together. Part of that special deal is shown after they attended the summer Hoshinome Cultural Festival, when Oka offered to dress and cos-play as a French Maid, and to go out on a date with Ueno in public dressed as such, to sooth his ruffled feelings about her serving in a Maid Cafe that day.
As shown in later chapters of the manga, Ueno, before he had met Oka, thought of himself as something of a playboy. This even to the point that he had a hefty crush on Tsubaki's older sister, Youko. Although several years older than Ueno, nevertheless, he would admire her, even taking a picture, without her knowledge or permission, of Youko wearing a sexy, bikini-styled, white two-piece swim suit the day that she took him and Tsubaki to the beach one summer. Eventually, Ueno 'grew out of it', and by the time he met Oka and they began dating as boyfriend and girlfriend, Ueno would devote all his attention to Oka, instead of Youko.