Have you ever been to Japan before? I think most people familiar with the situation would STRONGLY RECOMMEND that a visitor NOT rent a car unless you had some sort of really specialized need.

Having said that, my understanding is that an international drivers license will work fine for driving in Japan for visitors staying less than one year. What you may have read about is that as of a few years ago, Japan stopped accepting a US license on a reciprocal basis in order to obtain a Japanese drivers license, as would be needed by someone living in Japan. You used to be able to get a Japanese license by showing a valid US license and just filling out some paperwork, but now the holder of a US license is treated as if they've never had a license for the purpose of applying for a Japanese license and must qualify by taking an onerous driving test.