The two sisters, HyunA & Demi, are very well known to be part of the greatest cat clan alive. The two brothers, Hyunseung & Jonghyun, are very well known in the second greatest cat clan alive. First, let me tell you a bit of the cat world in Seoul.

Felinitritus - A non-contagious disease that can only be caught through digesting special plants in different areas in the world, most commonly known in South Korea.

When this disease has taken full affect, you will have two forms: A human form, and a cat form. For girls, they have lighter fur, for boys, they have darker fur. There are many different features in the human form for a person with Felinitritus, than a person without it. For example, people with Felinitritus seem to have either unusual colored eyes, or eyes that glow, or sparkle, more than it's supposed to. They also have a tendency to be more flexible and quick with their movements, unlike normal human beings.

But these four feline's are equipped with special powers, and they can't cross their territory lines, but falling in love isn't controlled by them.