Tanishi is a man with cheerful personality and is the frequent visitor of the cat cafe, often shows great interest in it.
Tanishi also seem to have a interest in one particular calico cat in the cafe, as shown when he frequently interact with it.

However, in one faithful day after the Nyandemic, he failed to escape the horde of cats (presumably due of the fact his ankle is sprained at the time after a car crash while trying to avoid hitting the cats) and eventually become one of them, although he is not hostile towards the duo after finding his way to them and even attempted to show trust by showing his belly, the duo leave him behind anyway. His fate remains unknown afterwards.

Tanishi is a muscular man with light stubble beard, red mohawk and always wears a pair of goggles, he wore a white shirt with green pants and boots.

As a cat, he is presumably a british shorthair that has yellow eyes and orange fur with stripes all over his body and white underbelly. Tanishi also kept his goggles, whether he intentionally brought it with him or simply don't care enough to discard it is unknown.

Tanishi also show up in the cover for both the first volume of the manga and anime, depicting him as a cat or being turned by large group of cats.

(Source: Nyaight of Living Cats EP1, Nyaight of Living Cats manga VOL 1)