Being (an extremely mild) Yaoi Genre story, the catperson who gets the most screentime is a Troubled, but Cute catboy.
The entire concept is Older Than They Think, with the first recorded mention of a modern catgirl (as opposed the the monsterlike nekomata and bakaneko) dating to a sideshow-like fair where there was a catgirl as one of the crew note Almost certainly someone in Cosplay. Catgirls often tend to be sexualized and/or have added Moe traits to better appeal to the audience. (These are usually found in Yaoi, and as a general rule tend to be Uke archetypes.) Catgirls oftentimes follow feline Animal Stereotypes associated with cats, specifically female ones. The catgirl is stereotypically female, though catboys do exist. What makes a catgirl different from an anthropomorphic catwoman or a Funny Animal cat is that she only looks superficially feline.
A catgirl is a Little Bit Beastly character that has mostly human traits (hair, skin and body type) but she has some physical features like a cat, usually the ears, tail, eyes, and sometimes claws or even a natural Fur Bikini.