Part of the silly Miss Mars Martian and Jadewave story is during one of their space adventures they end up on the moon and meet The Bunny Princess. I thought it would be hilarious if Serenity was a literal bunny.
If you don’t know, Japan has a saying about how on the moon the rabbit makes rice cakes (mochi), similar to how we talk about a man being in the moon. In Sailor Moon, Tsukino Usagi translates directly to “Rabbit of the Moon” as a pun on this saying. (my nickname also comes from this saying)