Once in Japan, you must carry your passport with you at all times. All foreigners (except those on government business) over the age of 16 are electronically fingerprinted and photographed as part of immigration entry procedures into Japan. This may also be followed by a short interview conducted by the immigration officer. Refusual to any of these procedures will mean denied entry to Japan.
Travellers entering Japan for longer than 90 days are required to obtain a Certificate of Alien Registration within 90 days of arrival. The ARC or gaijin card as it is known must be carried with you at all times in lieu of your passport. This card must be surrendered upon exit from Japan, unless you hold a re-entry permit.
The Secrets Of Speaking Japanese Fluently