I've heard mixed messages on this. I'm going to Japan on December 14th and plan to stay for most of the 90 maximum days allowed after entry.
However, what I heard is an airline can stop you from boarding a plane bound for Japan if you don't have proof of a flight ticket out of the country. Or if not the airline, it is possible that Japanese security will ask for proof of an ongoing ticket upon arrival.
The reason I wonder about this is because I would rather not have to choose the exact date that I will depart the country. I went to Japan once before, but during that instance I had already purchased a return flight so the whole issue never arose.
Any info you can provide on this will be greatly appreciated.