I've been watching Chobits and realized I could pull off Chi. (no my user name is not based off her.)
I have a Little Bo Peep costume, theater-quality made in pink and white. I would just need a wig and the ears, and I'm done! (And, maybe shoes.)
I'm battling between Umi and Chi right now, but if I can't get Yuuki, I might try to do Chi.