In this pack of Grimrock portraits, there is a file for a whole lot of characters from the Shin Megami Tensei: Persona series. The filenames and/or characters within this pack may be major spoilers for you if you haven't played the games.
To see what's included, go to my Grimrock Portrait Mega List. If anyone wants a character I missed, request it and I'll try to make it.
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.