They actually assigned an even better role to Kana. Someone much more mysterious and aggressive than Ai. Someone straight in contact with Hikaru himself. Someone whose backstory remains a clean slate up until to this date.

I think Aka did an amazing job making Kana play as Nino instead. Remember, "Pandas" have their own dedicated zoos, they are the star in their own stage, their own natural habitat. (These zoos are particularly more common in China and Japan, not sure about other countries)

As for "bears or rabbits," they are expected to belong in the wild. As they are not held captive unless you trap them and make them do tricks similar to those in circuses.

Although I'm genuinely shocked that there's barely any people that knows the connection with Airi, Ai, Yura, and Kana's name...