Uchi (内 うち?), better known in the English translation as Ucchi, is Tomoko's second year classmate. Because she could not form a group of five with her friends for the school trip to Kyōto, she along with Yoshida and Tamura are put in Tomoko's group.
Ucchi is first seen in Chapter 59 during Tomoko's second year of high school. She and Tomoko end up sitting next to each other on the bus to a baseball game but do not interact at all. Ucchi spends the whole ride chatting with her friends who are sitting behind them. This is a parallel to her actions in the future where end up in Tomoko's group for the school field trip (Chapter 69).
During this trip, Ucchi spends most of her time with her friends in Group Two and leaves the trio to their own devices. Occasionally she would come back to their room to gather her things or to check up on them but, at every visit, they were either hostile towards her or were doing something she considered weird, making her decide to stay away from them as much as possible. This feeling of avoidance applied especially toward Tomoko and even continued during school after the trip was over.
She spends most of her time in Chapter 69 chatting with her friends, for she does not want to associate with her field trip group, especially Tomoko. Due to a few comic misunderstandings and Tomoko's attempts to seem mature and experienced, Ucchi believes Tomoko is a pervert and even attracted to her. However, she seems to take a bit of odd pride in Tomoko's supposed interest in her as Ucchi is annoyed when it seems that Tomoko would act perverted towards any girl and not just her.
Ucchi is not completely innocent, however. Like Tomoko she has curiosity. While she has no interest in the other members of her field trip group, in Chapter 77 when she finds them all asleep in the room during dinner time, she notes to herself that she really does not care what they did that day but figures she should at least wake them. When she attempts to wake the difficult to arose Yoshida for dinner she takes the opportunity to touch her. Previously in Chapter 74, Tomoko apologized to Yoshida specifically for "pinching" her "nipples": "乳首つまんでごめなさい. . ." when she tried to wake her. This time, in her dream as Ucchi touches her, Yoshida believes it is Tomoko pinching her nipples again. She viciously elbows Ucchi in the stomach. A very hurt and angry Ucchi leaves and takes revenge by marking her entire group as present at dinner. In Chapter 84, she finds Tomoko in the bathroom after Tomoko took a few minutes to recover from accidentally grabbing Yoshida in her unmentionables. Ucchi immediately concludes that Tomoko is turned on by the sound of urination.
Nevertheless, later in Chapter 105, when she returns with souvenir treats and finds she has some left over, she seeks out the members of her field trip group including, "last, and certainly least," Tomoko to give them one.
She is blonde with a hairstyle that looks exactly like Yū's. Unlike other characters, her face looks like an
emoticon with dots for eyes, a similarity that Tomoko notes with irritation, referring to her as "Emoji Face." A few times, her face is drawn more conventionally when she becomes incensed, such as when she thinks Tomoko has been staring at her only to see she has been staring at some other girl.
Strikethrough episodes or chapters indicate the character was mentioned but did not make a physical appearance)
Ucchi has a complicated relationship with Tomoko. Due to several misunderstandings, Ucchi believes that Tomoko has a romantic obsession with her. In Chapter 93, she sees Tomoko at a mall with Yū, who bears a striking resemblance to her. Ucchi assumes the worst when she notices Tomoko buying underwear similar to the one Tomoko stole from her during the Kyōto trip. Because of this, she does her best to keep her distance from Tomoko; however, whenever she notices Tomoko taking an interest in another girl, Ucchi becomes bothered.
- Her last name is shown in kanji in Chapter 114 as 内 or うち in hirigana. This should be "Uchi" in English, but most fan translations render her name as "Ucchi," and the Japanese Wikipedia lists her character name as うっちー／内（うち）. This suggests that "Ucchi" is a diminutive or nickname for her last name. The English translations that give her last name as "Sasaki" for some reason add that name to two lists from the Field Trip. In the original manga her name is either cut off or covered by a speech balloon. This seems to fit with Tomoko's complete lack of interest in learning her name.