Good resources on offshore incorporation (taxes, legal work,...)? 19 years ago
From my understanding, as long as the what is sold is immaterial (e.g., membership, software) and doesn't need to be sent to a specific address, you don't need to register as doing business in the country where the good is sold.
So in this case, I think that he might not need to register for doing business in japan if he's not selling any tangible thing...
I'm not so sure though since I don't know how it is in japan.