The narrator is a voice of a man who had extensive knowledge of cats.

The narrator occasionally appears in order to share cat facts, especially to explain the context of the scene.

Although never directly appeared in person, he will describe the cat facts in similiar manner to educational videos and teach the viewers about cat facts.

This can range from cat anatomy, explaining their interaction with certain things, and their history.

(Source: Nyaight of Living Cats anime episodes)