Mitsukake's faithful pet cat. He's often used for comic relief moments commonly involving Miaka.

Spoiler

After Mitsukake's death, Tama-neko is put in the care of Chichiri.

Miaka names him in manga volume 12, a humorous portion that wasn't animated due to some time restraints. It starts with Mitsukake calling out, "Tama! Tama!" (In the Chinese version of the manga, the cat is actually named Tamahome...) Tamahome raises his hand in response, but Mitsukake says he was looking for his cat. He tells the others that Miaka told him to call the cat "Tama". (Source: ming-ling.net)