For Japanese citizens – Stay for more than 90 days consecutive
Japanese citizens do not need any visa to enter Switzerland due to the treaty of Establishment and Commerce concluded between Switzerland and Japan (only available in German, French and Italian).
However, you will need to apply for an “Assurance of authorization of staying permit” directly with the competent Office of Migration of the Canton of your future place of domicile before you enter Switzerland.
If you are married to Swiss citizens, the procedures for obtaining a staying permit should be started after you enter Switzerland. Even so, the Embassy is recommending you, to contact the competent Office of Migration of the Canton to get detailed information before you leave for Switzerland.
Some cantons inform about necessary documents on their website where the application form can be downloaded.