Alien registration
Foreigners who are scheduled to stay in Japan for more than 90 days must apply for alien registration at the municipal office of the area where they reside within 90 days of entering Japan.

(1) Registration procedures
In principle, a foreigner should go to the municipal office in the area of residence in person, fill in the official gapplication for alien registrationh form, which is available at the relevant counter, and submit this form, together with a passport and two copies of a photograph.

(2) Carrying the alien registration certificate at all times and returning it when leaving Japan permanently.
After your application for alien registration, you will be informed of the issuance of your galien registration certificateh within a designated period, and subsequently you must go to receive the certificate during that designated period. A foreigner who is issued an alien registration certificate must carry it at all times and show to Immigration Inspectors, Immigration Control Officers, Police Officers, and other officials if requested. Also, when leaving Japan, except when the foreigner has received re-entry permission, the foreigner must return the alien registration certificate to Immigration Inspectors at the airport or other port of departure.

Return home temporarily
If you are staying in Japan and you want to leave temporarily during the permitted period of stay and later return to continue the same activities, you should get a re-entry permit at a regional immigration bureau before departing Japan. Then you will not be required to apply again for a new visa as long as you enter Japan within the re-entry permit period.