CPK

CPK is an archive format used in the portable versions of  Persona games. It was developed by CRI Middleware and is the successor of CVM. All game data (except the executable) is stored in compressed CPK archives.

QuickBMS
aluigi's file extractor | QuickBMS has scripts in .bms format for CPK archives. Run quickbms.exe, select cpk.bms, and then select your CPK file. It will automatically extract the contents to the directory of your choosing.

CRI Packed File Maker
There are many ways to pack a CPK, but | CRI Packed File Maker creates CPK files from an extracted directory and can be used to view file information such as data alignment, number of files, and compression modes.