In this pack of Grimrock portraits, there is a file for a whole lot of characters from various Final Fantasy games. The filenames and/or characters within this pack may be major spoilers for you if you haven't played those games. Please take caution if you are not caught up and still decide to use this.
Extract the files and place them into this directory:
C:\Users\USERNAME\Documents\Almost Human\Legend of Grimrock\Portraits
Don't ask me how to install these on Linux or Mac. I've never tried to play games on either.