To be fair, all of you dumping on OP, there are keys on a Japanese keyboard that do not exist on a US keyboard, and many keys are in different places. If you plan to visit/live in Japan, it couldn't hurt to learn where all the keys are located.
It took me about a month living there before I figured out how to type certain things like quotation marks!
One of the keys switches between hiragana and katakana, IIRC.
Edit: Yup:
File:MacBookProJISKeyboard-1.jpg - Wikipedia, the free encyclopedia
See the 英数 and the カナ／かな keys. Also notice how many symbols are in a different place.
Something like 90% of typists are hunt-and-peck typists, so remapping keys is not quite useful for them.