Chibi Chibi appears to be about two years old, and can't really talk yet, though she knows a few simple words and likes to repeat what other people say. In the manga, she mostly imitates the ends of others' sentences; in the anime, she mostly says "chibi". Her red hair is always up in two heart shaped odango with little ringlets sticking out the sides, echoing the hairstyle of protagonist Usagi Tsukino.
In each series, Chibi Chibi immediately attaches herself to Usagi's family, whose memories are modified so that they believe her to be the youngest child—almost exactly what Chibiusa had done on her first appearance. Once again, only Usagi's memory is left intact, and because Chibi Chibi has the conversational skill of a toddler the Senshi are unable to question her.
Chibi Chibi eventually transforms, under her own power, into a Sailor Senshi. In the manga she is simply named Sailor Chibi Chibi, while in the anime she is called Sailor Chibi Chibi Moon. In the manga, Chibi Chibi transforms by shouting the words "ChibiChibi Crystal Power! Make Up!". This transition is never shown on screen in the anime.
The truth of Chibi Chibi's identity is very different in the manga from what it is in the anime, largely because the two series were being produced at roughly the same time.
In the manga:
Vova
