Sojourn for more than 90 days consecutive:
Japanese citizens do not need any visa to enter Switzerland due to the treaty concluded between Switzerland and Japan. Please refer to this link (only available in German, French and Italian).
However, you will need to apply for an assurance of authorisation of staying permit directly with the competent cantonal authority of your future place of domicile before you enter Switzerland. The contact addresses and Websites can be found on the following link.
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 will recommend you to contact the competent cantonal authority to get detailed information before you leave for Switzerland.
Some cantons inform about necessary documents on their Website where the application form also can be downloaded. Please note, that sometimes it might be quicker to look for the information on the Website than to make an email inquiry.