This tool, which is a part of the greater Kitserver package, is the most important tool in Neptunia modding at the moment. It allows you to extract game data from .pac files, which are used to archive all of the text/scripts, pictures and audio for Hyperdimension Neptunia Re;Birth 1-3, and Megadimension Neptunia VII. (This tool should be compatible with all of these games, despite what the screenshot may indicate; the archive format is broadly the same between games)

You still need Neptools and TIDTool to manipulate most of this data, however. And Neptools or NR1_packer to actually run whatever you modify. But this will help you get to the data in the first place.

This tool is extremely easy to use; drag the .pac of interest onto the executable. The whole archive will then be extracted into the same directory the .pac is in. It might take some time if you have a computer with a slower processor or hard drive, though.

The source code is included with this tool.