AboutYachiru is child-like in most aspects - she is small, cheerful, energetic, and carefree most of the time. She is often seen latched onto the back of her captain, Kenpachi Zaraki ("Ken-chan" as she calls him, "Kenny" in the English Dub and manga), just over his left shoulder, and is somewhat territorial about this position. She is surprisingly intimidating at times, especially when annoyed. Like Kenpachi, she has no sense of direction, but even so, he relies on her for directions. Yachiru resents being criticized in any way and will often attack the perpetrator. Further reflecting her child-like nature, Yachiru likes to give people nicknames. For example, she gave Makizō Aramaki the name "Maki-Maki" and later when he reminds her of that name, she finds it funny. She later renames him "mini-mustache". She also calls Ikkaku Madarame "Baldy".
Yachiru's favorite free-time activity is eating sweets, though she will eat pretty much anything. She attends Head Captain Yamamoto's tea sessions , Captain Unohana's ikebana lessons, and also Captain Kuchiki's Calligraphy Club, but only to eat up the snacks and cakes served during these occasions and then disappear within moments.
It is also known that Yachiru's specialty is infiltration, which she uses mostly for mischievous deeds. During the time Kenpachi takes his usual afternoon nap, she goes to play around Seireitei. She appears to have dug secret tunnels through the Kuchiki house, as she was seen searching for Ichigo Kurosaki ("Ichi" as she calls him), to show them to him. The tunnels are shown again when Lieutenants Isane Kotetsu and Nemu Kurotsuchi try to take a photograph of Byakuya Kuchiki.
Yachiru is the president of the Shinigami Women's Association, and holds its funds as such, spending it mostly on toys and candies. She stores her "treasures" in the hideout on the Kuchiki grounds mentioned above. It seems that she uses the whole Association to order the other members around, who are made to do various, mostly childish pranks and other "tasks" to please her.
Yachiru seems to have a little-girl crush on Byakuya Kuchiki. She refers to him by affectionate nicknames like "Bya-kun" and "Byakushi," invites him to come eat with her (which she never asks anyone else) and at one point is seen offering him her drool-covered lollipop. Byakuya seems to find her crush annoying and mostly ignores her, though he apparently keeps buns on hand to jam into her mouth if she gets too assertive. In a recent omake, she has been seen dressed up in a cat costume, catching the koi in Byakuya's pond and releasing them in Ukitake's pond. While visiting Jūshirō Ukitake and "helping" him finish his food, Rukia mentions that there are no more koi in the pond, which Byakuya is upset about.