Сакамото

A black cat who wears a scarf created by the Professor, which allows him to speak. Being technically older than both Nano and the Professor, he speaks in a condescending tone towards them, though he occasionally succumbs to his catlike habits.

In the last episode, it is revealed that Sakamoto used to be Nakamura's cat and was called "Taisho". Sakamoto does not want to return to Nakamura because she did not take good care of him, even though she had good intentions.