A key point to consider is that regardless of where you incorporate, you still have to work within the legal framework of where you're doing business. For example, if I incorporate in Nevada or Delaware and I'm located in California, I have to file paperwork with California to get permission to do business in the state, and I have to pay California taxes. Check with a local attorney about Japan's legal requirements for foreign companies to work locally. And, if it satisfies your needs, then Delaware and Nevada are good options. I used corporate.com and I'm happy with their service. Of course, they'll only do the basic filing for you; after that you still need to do more paperwork, especially around taxes.