My Kitten girlfriend ~Nyan Kano~

The protagonist is a working man who loves cats. One day, he stumbles upon a cute cat abandoned in front of his office building and decides to take it in as his own. Unfortunately, after a few days it runs away from home. The protagonist is disappointed but after a few days spots the same cat on the side of a road. It looks like the cat is trying to take him somewhere... The cat's behavior is suspicious but the protagonist decides to follow it anyway. The cat leads him into a cave and standing inside is a beautiful young girl. The cat that he saved had become human! The girl says that she wants to repay him and takes him to a mysterious world of creatures like her...