Moon is the round cat in Whispers of the Heart. He's a crucial element of the story. In the manga, there were two cats, but they bore too much of a resemblance to both Luna from Sailor Moon, and Jiji from Ghibli's own Kiki's Delivery Service. A Ghibli rep joked that this combination of two cats is why Moon is so plump.

Moon is mostly cream-colored but has one brown ear. He likes to tease dogs, and takes the train by himself. He seems to have some sort of mystical connection to Baron, but doesn't belong to the store where Baron resides. Instead, he travels all about. Different people call him different names. (They probably all feed him, too, which is probably really why he's so fat.)