What program were the characters created with?
Not a programs as such, they were drawn by artists. (Well, I am sure they might have used a program for that - but nothing like Daz3D, Koitaku, HoneySelect, PlayHome and what else there is specifically designed for this).
Yep we need a save or gallery, because the pictures looks like this if we use unren
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Gallery will probably come, as discussed earlier, but only once the game is finished. Unren is indeed not going to do you any good since these are multi layered raw images which will then have facial expressions, piercings and similar superimposed, so (almost?) none of the images you see on screen exist as such but is composed of individual parts.