Anthy's pet (whom she will only refer to as friend, but may be more properly described as a familiar). He is a small marmoset who acts as comedic relief. However, he also acts as an omen of bad fortune in certain episodes.

ChuChu is drawn much furrier by Chiho Saito in the manga than he is drawn in the anime, the anime itself making him look more like a mouse than a monkey.

(Source: Wikipedia)