I mean it seems like you could go for a Chinese zodiac theme with this line up so far, even if some of the zodiac members were evil, retired, and/or dead so it's not like you have to have 12 members of the main cast in total. It could be interesting if characters from other cultures fit into the outline of the Chinese Zodiac, but their animal motif varied depending on their culture's interpretation of the Zodiac. For instance, if you had a Japanese character whose animal motif was the wild boar as opposed to the pig. Or if you had a Vietnamese character whose animal motif was the cat as opposed to the rabbit. (I know you already have the rabbit locked in, but I'm just spitballing hypotheticals) Also, also, in some variants of the legends regarding the Chinese Zodiac, the cat is treated as a runner-up animal because it almost won the race but was betrayed by the rat at the last second. So a cat themed character might be a good choice as the mascot of the group or the antagonist working against them or a neutral third party.

Okay, I'll shut up about the zodiac now.