Toshibou

Toshibou is a very fat cat used to be Tomoe's pet. Despite his weight, Toshibou is pretty agile, and actively involved in the roommates' adventures. He may come to the rescue in difficult moments, and it seems that this mysterious cat understands human speech. Tomoe can somehow communicate with Toshibou. At least, she thinks so.

Spoiler

In fact, Moe is not even close to what Toshibou says. Moreover, Toshibou is not "he" but "she", and she calls herself Nina Francoise.