If you wish to marry in the U.S., there are two major things you'll need to learn more about:
Marriage requirements in the state where you'll get married and
How to get the proper visa for your fiance/fiancee before s/he enters the U.S. for the wedding.
You may need a copy of your birth certificate or other vital record to marry. Here's how to obtain vital records in the U.S.
There are several commercial sites that list the requirements for most venues in the U.S.
Nolo Press
World-Wide Weddings
My Counsel
You can also look up your local authorities (start with the Yellow Pages' entry for the place you'll marry).
Your Japanese fiance/fiancee may have requirements that will have to be met for the Japanese government in order to marry in the U.S. While the U.S. Embassy in Tokyo does not have this information, the Japanese Embassy and Consulates in the U.S. should be able to help. Start online with the Japanese Embassy, or use the Yellow Pages to locate a Japanese Consulate in a major city near your home.
All U.S. visas are identified by letters and numbers. You'll need to help your fiance/fiancee apply for a K-1 visa. This visa allows your fiance or fiancee to travel to the United States, marry you, and then adjust status there to become a legal permanent resident (LPR) in the U.S.
If you and your fiance/fiancee are in the U.S., and have already married, you should contact the Immigration and Naturalization Service (INS) office nearest your home to discuss an adjustment of status for your new wife.
If, after the I-485 has been filed, your spouse needs to depart the U.S. prior to adjustment, advance parole must be obtained (see Form I-131). Failure to obtain this prior to departing the U.S. will result in the abandonment of the application for adjustment. If your spouse departs the U.S. without approved advance parole, s/he will not be able to return to the U.S. until the U.S. citizen spouse files a new I-130 petition, and you go through the immigration process again.
Unfortunately there are people who, usually for a tidy sum of money, will offer inaccurate or bad advice
For example, some travel agents will advise you that a tourist visa is the way for your new spouse to enter the U.S. to begin your new life there. Such advice can, at best, waste time and distract you from the necessary paperwork. At worst, it can lead to fraudulent statements that can see your new spouse found ineligible for any visa to travel to the U.S. It is always the type of travel-- a short visit or a new life living and working in America-- that governs what visa is appropriate.
K-1 and immigrant visas do require more time and preparation than a simple tourist visa, but, in the end, allow you and your spouse to begin your new life in the U.S. without the worry and hardships that fraud can place on your relationship. If you begin early, and follow the instructions carefully, your new spouse can begin life in the U.S. with the proper visa. Let us help you get your new life off to the right start!