Chu-chu is a member of one of the native species of the planet. Hundreds of years ago Solaris released a Limiter that eventually reduced their great size to something more... managable for Solaris, hence the "stuffed animal" like creature you see in the portrait. Apparently, some time during the Diabolos Invasion, Shevat took this race of little beings in, and now they are only seen in the aerial city itself.
Age: 1.25 years
Clothing size: n/a
Shoe size: n/a
Ring size: n/a
The character (according to the remnants of a back story in Shevat's item shop) was supposedly taken to the surface by Wiseman for some unknown purpose. She later appeared in Margie's posession, and was taken on board the Yggdrasil during her escape. Upon meeting Fei, Chu-chu developed an instant crush on him, and decided to help with his cause in any way she could.
She is supposed to be the most beautiful girl of her kind. I don't know why Fei doesn't see it. ^.^ But at sixty pounds, I don't care how pretty she is, Margie would not be toting her around like a stuffed animal! Her name is supposed to be the sound mice make - 'chu' - and you can see a 'Chuchu' in Utena who demonstrates this.