DDS2Tool Initial Release

DDS2Tool isn't a tool for Digital Devil Saga 2, but it IS a tool for extracting DDS images from DDS2 archives. In Persona 5, bustup BIN files contain typically 2 DDS files per frame.
Atlus's bizarre way of avoiding image compression artifacts was to save one layer of the frame with DXT1 compression, and another with DXT5. In-game, the DXT1 is overlayed ontop of the DXT5 to give the illusion of a full image being rendered. Each 2 slices of the frame are stored together as a DDS2 file, hence the name of the tool.

By supplying the path to a BIN file, you can extract all DXT1 and DXT5 images from the BIN. They will be saved to a new folder for editing.
Note: This does not work on the early, unused portraits from the Persona 5 trailer.

By supplying a path to a folder with DDS images, you can generate a new BIN file.
Note: This will probably only work in-game if you keep the filenames the same, and don't add or remove DDS files. I'm not sure at this time if saving the DDS file with a different type of compression will matter, but try to stick to DXT1 and DXT5 if possible.

And finally, by supplying a path to a folder with BIN files, you can mass-extract all the DDS files. It will automatically skip any unused ones using DXT3.