The chibis are aligned to match the Chinese zodiacs as well as possible. Even the order is correct:
Rat: Nazrin
Ox: Keine
Tiger: Shou
Hare: Tewi
Dragon: Meiling
Snake: Kanako
Horse: Komachi
Ram: Patchouli
Monkey: Iku
Rooster: Mystia
Dog: Momiji
Pig: Yuugi
Obviously some of them are fillers due to lack of better alternatives. Maybe they’ve been selected according to the animals’ characteristics. (→Wikipedia article)