I occasionally ate a Kit Kat bar in the USA. They look like this:
In Japan there have been more than 300 types of Kit Kats made since 2000. Many are limited edition, seasonal, or regional flavors. At this link you can check out some of the flavors by clicking on the arrows to the right or left. I've tried the macha flavor, but I don't think I've had any of the others.
Kit Kats are often used as a type of good luck charm for students taking entrance exams because of the similarity of the name Kit Kat to the Japanese phrase Kitto Kattsu, which means "you will surely win".