Sorry if this turned into a book, but I like to be thorough and I used to do Mac support :p

1) Install the game (simple enough)

2) You’ll need to launch the game and start a new game, the proper portrait folder will not be created until you do so.  It’s ok to leave the game open for the rest of this if you wish, I did.  You could get away with not doing it and following the instructions, but I just like being able to see the Portrait folder where it's supposed to be to know I'm in the right place.

3) THIS is the voodoo part.  I will be pointing towards some information to make a temporary change to your system to allow you to see hidden folders.  You will need to do a command in Terminal which may seem a little scary, but as long as you type in what the instructions tell you to, you’ll be ok.  And if you make a typo somewhere, most likely nothing will happen.  BUT this is where I have to at least say “if you break it, it’s not “our” fault”.

https://ianlunn.co.uk/articles/quickly-showhide-hidden-files-mac-os-x-mavericks/

That said, the link I’m giving here is the instructions I followed. You can ignore everything on the page once you get to the “Show/Hide Hidden Files using Terminal Alias” section.  Once you’ve moved the portraits over, you can do the “NO” version of the terminal command and after you relaunch Finder again, everything will go back to looking like normal.

So, follow the instructions, open Terminal, run the “YES” version of the command, and relaunch Finder.

4) Now you need to get into your home folder.  Several versions back, Apple made it harder to “accidentally” do that.  This may vary on OS versions (for anyone else following along), but what you can do is open a finder window.  Click on the word “Finder” in the top left of your screen and choose “preferences”.  Click on the Sidebar tab.  You’ll see a list of checkboxes, one of them under “Favorites” should have a House icon with the name of your account next to it.  Check that checkbox.  Close the preferences window.

Now in the Finder window, under Favorites, you’ll see that house icon again.  Click on it.  And welcome to your home folder.  DON’T delete or move anything from that folder unless you know what you’re doing.  That’s why Apple semi-hid it away a few years ago, to just prevent  potential accidents.  If you’d feel safer, at the end of all of this you can just reverse these finder instructions to make the home icon go away.

5) Now in your home folder, you may see a lot of items that are faded out, those are all the hidden things that you wouldn’t normally see without using the terminal command.  You are looking for a folder called “.strive2” (potentially down the road, if the installed game name changes, this folder may have a different name).  Go ahead and open/expand that folder and you should see a “Portraits” folder inside. (There’s also a “bodies” folder for the full body pics, if people have those).  If that folder isn’t there, it’s probably because you haven’t started a new game yet.

Assuming you’ve already extracted the portraits folder from the download, you can drop the downloaded portraits folder into the “.strive2” folder.  To be clear, you’re not dropping portraits into portraits, you’re dropping portraits into “.strive2”.  Doing so, you should get a prompt that I forget the exact verbiage, but should say something to the effect of “do you wish to replace (or merge, I forget) the portrait folder”, choose yes (or whatever the affirmative action button is).

This should copy all the folders from the download into the proper place.  So when it’s done, if you go into the Portraits folder in the .strive2 folder, you should see all the “bunnygirl, batgirl, etc…” folders there.

6) Almost done! If you have the game running, choose one of your slaves, open the customization tab, and click the Portrait button.  I believe the portraits should show up at that point, if not try the “reload portraits” and they should show up.  At this point you should be ready to run the “NO” version of the terminal command which will hide the hidden things again.  And then bookmark this info should you have to do this again:)

I just started playing a few days ago, thanks Kotaku.

Now...I've said all that, and that's the long way to do it.  But there may be better ways to do this.  I see in the Portraits menu, there's a button for "Select folder".  But the game engine uses it's own menu, not the OS's, so you can't just unpack the portraits in the downloads folder and say point the game at it.  Not easily at the last.  Macs can be simple, except when they're not.