Please check that your passport will be valid while you are in Japan and still be valid upon departure, but the remaining period of validity doesn't have to be six (6) months and that you have the relevant visa if required. Please note that Australian citizens travelling to Japan are not required to obtain a visa to enter Japan if the trip is for less than 90 days and when the visit is for tourism, a business trip, a conferences, to see relatives and friends, etc. However, when foreign nationals, including Australians, engage in paid activities in Japan a visa is required regardless of the length of stay.