Yotsuba is depicted as a small girl with green hair styled in four pigtails, resembling her namesake, a four-leaf clover. She possesses a carefree and energetic personality, finding joy in simple things as she learns about various aspects of daily life. In the Japanese text, Yotsuba's dialogue is written without kanji, making it appear simpler and more childlike, and uses a typeface that conveys a sense of high intensity. Her boundless energy is often remarked upon by other characters, particularly members of the neighboring Ayase family. Her father describes her carefree nature by saying, "She can find happiness in anything. Nothing in this world can get her down." However, when deeply frightened or upset, she does cry, and she has an inexplicable fear of anything resembling a bullseye.
At the beginning of the series, Yotsuba is shown to have very little knowledge of the world around her, even for a young child. Things like swings, doorbells, cicadas, and air conditioners fascinate and confuse her, though she remains unfazed by her lack of understanding. She sometimes mispronounces new words and invents neologisms, such as "Yotsubox" for "Yotsuba's Box," and often repeats phrases spoken by adults in unexpected contexts. Yotsuba is frequently seen drawing, though she is not as talented an artist as she believes herself to be, and she excels at swimming.
The series offers few details about her life before the story begins. Yotsuba is an adopted child, with her birthplace unknown to the reader, although she claims she is from an island "to the left." Koiwai, Yotsuba's adoptive father, says he met her as an orphan in a foreign country and ended up raising her as his own; she is sometimes mistaken for a foreigner by strangers. When asked about her mother, she doesn't comprehend the question, and she is confused by the concept of having two sets of grandparents. Before moving to her current home, Yotsuba lived in the countryside with Koiwai and his mother. Initially, she tells Fuka Ayase that she is six years old, but her father later corrects this, stating she is actually five.
Yotsuba has never attended school and, at the start of the series, does not understand what a grade is. In chapter 35, she struggles to grasp repeated explanations of homework.
