She has a carefree and energetic personality, taking delight in simple matters even as she learns about all manner of things in her daily life.

[1][2][3] From chapter 3 onwards, Yotsuba's dialogue in Japanese is written without kanji, making it seem simpler and more childlike,[4] and in a simple, large, and bold typeface, which gives the impression that she is speaking with high intensity.

She occasionally mispronounces new words and creates neologisms, such as the name for her "Yotsubox" (よつばこ, Yotsubako) a portmanteau of "Yotsuba" and "box" (はこ, hako) that she uses to keep special things and her "scapbuk" (scrapbook).

She often repeats, in incongruous ways, phrases spoken by adult characters around her without fully knowing the meaning, so she sometimes says vulgar words.

For example, one wrote, "Yotsuba’s wide-eyed awe at each discovery, from the idea of a milkman to learning how to catch fish, is both inspiring and infectious.

"[15] A reviewer at Anime News Network wrote, "What is really special about Yotsuba, though, is that newness with which she, as a child, sees the world.

"[16] Johanna Draper Carlson, long-time comics reviewer for Publishers Weekly, said that "Yotsuba is a sponge of a character, with infinite possibility as she learns about life.

"[17] Another claimed that "Yotsuba Koiwai's adventures are ... a lucid and charming look at the world through a child's eyes, as she gets into scrapes that remind us all of our own childhoods (if only through manga-tinted glasses).

"[1] On the other hand, Tom Spurgeon claimed Yotsuba is "an idealized kid of that early age, retaining a wide-eye wonder and furious energy, minus the things that crop up at that age like cruelty and deception"[3] and a reviewer in Newtype USA said that "Her hijinks are sweetly innocent, like a cuter, more naïve version of Dennis the Menace minus the 'menace'.