I've gotten it to work! Let me know if this helps anyone else out.
First, I downloaded one of the Fallen Doll game files. The one I downloaded is depot_1810921, but the torrent one will work too.
First, navigate to depot_1810921\Paralogue\Binaries\Win64 (depot can be whatever the game file name is)
Next, delete "Mindflayercertificate". Make sure to windows search (Windows Key + S) and search "run", type "certmgr.msc", which should pull up certmgr. This is a program already on your windows machine. Click "Action", Find Certificates, and type "projecthelius". Delete any certificates there.
Next, Navigate to the game folder. Mine is "epot_1810921". Run "FallenDollLauncher.exe".
When you get to the main game menu and it runs, tab out and head back to windows file explorer. Navigate back to depot_1810921\Paralogue\Binaries\Win64. Run Mindflayer.desktop.exe. It should open a few dialogues to create a certificate. If needed, run in administrator mode. It then should open a second instance of FallenDoll.
You know you've accomplished everything right if, on the yellow menu on the right, it reads mindflayer. You should be good to go!
Run Harem mode. If you encounter an error saying to restart and connect to steam, follow the steps below
Go to "depot_1810921\Engine\Binaries\ThirdParty\Steamworks\Steamv147\Win64" (again, depot is just the name of the game folder), and replace steam_api64.dll with the attached file below.