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Koharuko Koiwai
Japanese 小岩井 小春子
Romanized Koiwai Koharuko
Gender Female
English voice actor None
Japanese voice actor None

Koharuko Koiwai (小岩井 小春子 Koiwai Koharuko) is a character from Yotsuba&!. She was first mentioned in volume 13 by Yotsuba's grandmother and made her first appearance in volume 14, during Yotsuba's trip to Tokyo. She was the one who sold Yotsuba's father and Yotsuba their car.

She is presumed to be the younger sister of Yousuke (Yotsuba's father), and therefore Yotsuba's aunt. She refers to Yousuke as onii-chan, which means "older brother." She lives in Tokyo and does not interact with the rest of the Koiwai family very often.


Koharuko is a tall and slim young woman, close to her brother in height. She has long black hair which she wears in a ponytail and rounded square glasses.


Yotsuba described her as "someone who often bumps into a corner with her hands or feet", indicating she may have a clumsy nature, though this has yet to be shown explicitly. Koharuko also says that she decided not to take Yotsuba to eat monjayaki since she was worried about Yotsuba burning herself on the hot griddle, as she was sure she herself would do so.

Overall, her personality resembles that of her brother and Yotsuba's grandmother (who is presumably her mother as well), as she is calm, serious and cares a lot about her family, despite not showing strong emotions outwardly most of the time. Like her other family members she also has an eccentric side, shown when she fiercely defended her decision to start with eating the main dish rather than an appetizer at a buffet, much to Yousuke's befuddlement. She is more laid-back than Yotsuba's grandmother, but stricter than her brother, and shares a deadpan sense of humour with both of them. In addition, she appears to have perfectionistic tendencies, openly mourning her inability to come up with an idea for what she, Yotsuba and Yousuke should have for lunch that is flawless in every single way. As she can change her mind on a whim, such as about whether or not eating ramen for lunch in Tokyo would be a good idea, she comes across as being fickle as well.

She seems unused to dealing with children as she constantly keeps a serious expression on her face and is direct with her words when speaking to Yotsuba. She often gets confused with Yotsuba and Yousuke's antics, such as when she was about to give them their new car and Yousuke told her he and Yotsuba were in Harajuku, instead of at their intended meeting spot, since Yotsuba had expressed a desire to go there.


Yotsuba Koiwai[]

Koharuko has a positive relationship with Yotsuba, her niece. Like her brother, Koharuko enjoys tricking Yotsuba for fun, as she told Yotsuba her suspicions about dressed up humans being aliens were true. Judging by her decision anxiety about what Yotsuba would most like to eat for lunch when she and her father visited Tokyo, Koharuko appears to care deeply for her niece and take her feelings into consideration. Yotsuba is very fond of Koharuko, as she was unwilling to say goodbye to her aunt when they were about to part ways in Koharuko's only appearance in the manga to date. Yotsuba invited her to come over to the Koiwai Residence for dinner, though Koharuko declined the offer. Yotsuba was informed that Koharuko would instead join hers, her father's and grandparents' New Year's celebration. It is likely that Yotsuba and Koharuko used to meet more often when Yousuke had just adopted her and the two of them were living in the country with his mother.

Yousuke Koiwai[]

Koharuko seems to get along well with her older brother Yousuke, due to their similar personalities. However, Koharuko occasionally scolds Yousuke for what she perceives as questionable parenting, such as when he told her via text message that he and Yotsuba had already eaten crêpes despite the fact that the three of them had decided prior to meet up for lunch shortly thereafter. She was also dumbstruck upon finding out that Yousuke had lied to her about him and Yotsuba not having eaten cotton candy, and showed skepticism when Yotsuba informed her of the odd slapdash dishes her father makes for her as well as the fact that she considered them to be just as good, if not better, than the food at a fancy restaurant. Despite these differences, however, they can easily compromise with each other and come to mutual agreements, as well as move on from awkward situations, because of both being mild-mannered. She can be mischievous around him as well, like when she took Yousuke and Yotsuba to an expensive restaurant and withheld the fact that she was expecting him to pay for everything until they were already seated, as she correctly guessed he would not protest.


  • The name Koharuko means "small" (小) (ko), "spring" (春) (haru), and "child" (子) (ko).
  • Koharuko's surname Koiwai means "small" (小) (ko), "rock" (岩) (iwa), and "well, mine shaft, pit" (井) (i).