The "RJ" prefix is used by DLsite , a major Japanese marketplace for indie (doujin) games, manga, and audio.
While finding these files online is common, purchasing the original from DLsite ensures: No risk of malware or viruses. Updates: Access to patches and bug fixes. H-RJ01019462.rar
Right-click the file and select "Extract Here." If the file is password-protected, the password is often the site URL where it was downloaded or simply the RJ-code itself. The "RJ" prefix is used by DLsite ,