相关规则
Japan
Practice Relating to Rule 125. Correspondence of Persons Deprived of Their Liberty
Japan’s Law Concerning the Treatment of Prisoners of War and Other Detainees in Armed Attack Situations (2004) states:
Article 83
Correspondence with detainees may not be prohibited or restricted, other than that which is provided for in this Section.
Article 84
(1) The prisoner-of-war camp commander may, pursuant to an Ordinance of the Ministry of Defence, impose restrictions necessary for the adequate pursuance of the internment concerning the manner in preparing and the number of letters, and the procedures for sending or receiving letters of detainees; provided, however, that this shall not apply to letters that the prisoners’ representatives or the assistants to the prisoners’ representatives send to national or local government agencies, protecting powers, the designated Red Cross International Organization, or designated assisting organizations and that contain matters under the authority of the prisoners’ representatives or the assistants to the prisoners’ representatives pursuant to the provision of Article 80 and other provisions of the Third Convention [1949 Geneva Convention III]. 
Japan, Law concerning the Treatment of Prisoners of War and Other Detainees in Armed Attack Situations, 2004, Articles 83 and 84(1).