Uchi (内 うち?), better known in the English translation as Ucchi, is Tomoko's second year high school 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.
In Chapter 77, Ucchi once took revenge on her group after finding them asleep in their room before dinner time. She originally tried to wake them up but Yoshida mistakenly elbowed Ucchi in the stomach, so Ucchi said all of her group was present at dinner so they wouldn't get any later. She clearly cared about her group, but after an accident what little affection that was there quickly left.
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, which is a very odd thing to assume.
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. It is not directly stated why she did this, but she might care about her group to some extent.
In later chapters Ucchi has been shown to be obsessed with Tomoko, as her stalking of the girl clearly shows. Surprisingly enough, Tomoko never notices nor cares. Ucchi is distraught when she is not put in the same class as Tomoko for her third year at school.
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. In recent chapters, Ucchi's avoidance of Tomoko has disappeared and is replaced with an obsession with Tomoko, such as creepily lying in wait behind her locker for Tomoko to put chocolate behind her locker and also attempting to go to Tomoko's bus stop to try to get Tomoko to lean on her on the train.
- 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.