Always Carry Your Passport in Japan
Always Carry Your Passport i...

Buisness as usual: A police officer takes a passport from a passenger at Narita International Airport, Chiba Prefecture, during a security check in August 2013. Tourists staying in Japan for less than three months must always carry a passport. | KYODO

Also police has a right to search your possession in Japan without court order. Well, actually they do not, but they do ask you "If it is okay." ... If you say "No" ... you can get detained. If you resist, you will be searched.