CVM is an archive format used in the PS2 versions of Yakuza and Yakuza 2. It was developed by CRI Middleware and based on ISO9660. It is also known internally as "ROFS" format. Essentially, they are ISO files with a special header (0x1800 bytes).
List of the Games
These are the list of the game with .CVM files. Includes:
Ryu Ga Gotoku: Kenzan! and Yakuza: Dead Souls are not encrypted.
Now you need to extract the ROM and cvm_tool on the same folder
Run Command Prompt as administrator, then type
cd /d your_folder_directory
Then use the following command to output an ISO file for you to edit:
cvm_tool.exe -p qi2o@9a! split OGRE.CVM OGRE.iso OGRE.hdr
Use this to repack your CVM back:
cvm_tool.exe -p qi2o@9a! mkcvm OGRE.CVM OGRE.iso OGRE.hdr
The same principle goes to other .CVM files