The assets are stored in an 11gb file: SAOFB\Content\Paks\SAOFB-WindowsNoEditor.pak
There's also a 700kb file in that same directory: SAOFB-WindowsNoEditor.sig
The only speculation I have found about this is from a different forum with someone else making such a request, the reply they got:
If it is like the other Bandai game that I have experience modding, then the pak decrypt tool won't work even if you do find the RSA encryption key in the exe or dll files.
The reason is the format of the compression changes slightly game to game. So the tool has to be re-written.
I am making an "educated" guess here. I haven't checked.