United States of America citizens, only need a valid passport to stay in Japan as a tourist, up to 90 consecutive days without visa. No other document is required.
Most of western countries benefit from the same rules (Canada, Western Europe, etc.). Swiss citizen can even stay up to 180 days.
There are other visas for a longer stay in Japan, such as the Working Holiday Visa, granting the right to stay up to one year and even work in the country.
Keikaku cannot help travelers with the visa application procedure.