All foreign visitors are required to have a valid passport. If you are simply visiting Japan, chances are that you will not need to obtain a visa. Those from the United States will not need to obtain a visa if they are in the country to sightsee, participate in sports activities, family visits, short academic study, or attend business meetings for a period of 90 days or less.
United States citizens visiting Japan are not required to obtain a visa prior to arrival.
If you are a US citizen who will be in Japan for more than 90 days and need a visa, you must apply in person at a nearby Japanese embassy or a consulate. The following documents must be submitted whatever the purpose of visit you are going to make:
Two passport photos taken within the six months previous to the date of application. Two official visa application forms, available at the embassy or consulate documents certifying the purpose of the visit.