If you are married to a Japanese national and want to live in Japan with him/her, you will need a visa for a Spouse or Child of a Japanese National. It is important that your marriage is legal in Japan. De facto partners cannot get a visa for a Spouse or Child of a Japanese National.
Can you get Japanese citizenship through marriage?
Simply marrying a Japanese citizen does not automatically grant Japanese citizenship to a foreign national. Attaining Japanese citizenship must be done though the normal naturalization process. However, marrying a Japanese citizen does allow the foreign national to immediately obtain a spousal visa.
What happens when you marry a foreign citizen?
Marrying a foreigner for money is illegal, and those participating in immigration fraud can face up to five years in prison, a fine of up to $250,000, or both, according to the U.S. Code § 1325: Improper Entry by Alien.