Yachiru Kusajishi

is the Lieutenant of the 11th Division in the Gotei 13, under Captain Kenpachi Zaraki.

Character Outline
Yachiru is child-like in most aspects, as she is small, cheerful, energetic, and carefree most of the time. She is often seen latched onto the back of her captain, Kenpachi Zaraki, 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, even though 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. The anime suggests that Kenpachi simply walked in and killed the former 11th Division captain, thus becoming the current one, so it stands to reason she became a shinigami at the same time. In an interview, Tite Kubo mentioned that he plans on revealing Yachiru's namesake.

In golden cup 172, she appears to have dug secret tunnels through the Kuchiki house, she was searching for Ichigo, "Icchi", to show them to him. The tunnels are shown when Lieutenant Isane Kotetsu and Nemu Kurotsuchi try to take a photograph of Byakuya Kuchiki.

Synopsis
Yachiru is first seen directing Zaraki through the Seireitei (albeit badly). She then becomes quite fond of Ichigo and his friends after Ichigo defeats Zaraki. She leads Ganju Shiba, Chad, Orihime, and Uryu Ishida to where Rukia is being executed. Later when Zaraki enters Hueco Mundo, she follows him and stands back while he fights Nnoitra Jiruga.

Shinigami Powers
Enhanced Strength: Despite her child-like appearance, Yachiru is apparently quite strong, since she is the current lieutenant of the combat division within Soul Society. She is strong enough to lift Kenpachi and leap between buildings while carrying him.

Enhanced Speed: Yachiru is also incredibly fast despite her size, running from the ground-level area of Seireitei to the mountain that holds the execution grounds in a fairly short period of time.

Enhanced Spiritual Energy: She is also capable of emitting a large amount of spiritual power when angry, which forms into a large, pink, angry cat face.

She also seems to be immune to her captains spirtual pressure

Zanpakutō
The name and ability of Yachiru's zanpakutō are both unknown. She carries her zanpakutō around with a loose cord, rather than at the sash of her uniform. Her zanpakutō's scabbard is also unusual in that it has a pair of wheels for transport. According to Yachiru's profile in volume 13, these were installed by Ikkaku Madarame, who turns out to be handy with tools, after she continually pestered him to do it. It also has a child-like flower pattern on the crossguard.