Yotsuba Koiwai's Story

Yotsuba&! is centered on Yotsuba Koiwai, a five-year-old adopted girl who is energetic, cheerful, curious, odd, and quirky—so odd and quirky that even her own father calls her strange. She is also initially ignorant about many things a child her age would be expected to know, among them doorbells, escalators, air conditioners, and even playground swings. This naiveté is the premise of humorous stories where she learns about, and frequently misunderstands, everyday things.

At the start of the series, Yotsuba and her adoptive father, Koiwai, relocate to a new city with the help of Koiwai's best friend, an impressively tall man nicknamed Jumbo. Yotsuba makes a strong impression on the three daughters of the neighboring Ayase family, Asagi, Fuka, and Ena, and many of her misadventures come from her interactions with them.

The series has no continuing plot—the focus of the stories is Yotsuba's daily voyage of discovery. Many chapters take place on successive days (for details, see List of Yotsuba&! chapters), so that the series follows, almost literally, the characters' daily lives. The tone can be summarized by the motto, used on chapter title pages and advertising, "Today is always the most enjoyable day" (, Itsu de mo kyō ga, ichiban tanoshii hi).