Sorry for the delay! The issue has been fixed in New V.1.1.4 - Bugs Fix + Adds. You can press F4 in the menu to delete your current save and restart the game. After playing again, you should be able to unlock the characters normally.
However, since you’ve already played through those two levels, I created a bug-free save file for you.
Instructions:
1. Download the new save:
2. Replace the save file in the folder:
C:\Users\Your User\AppData\LocalLow\Sweet Heart Games\Succubus Heart's Domination
(Replace "Your User" with your Windows username.)
3. Play the game!
Let me know if you encounter any more issues! 😊