Do you have a previous save file?
This is my first time seeing this ObjectManager error, but it looks like it could be related to my changing around the data for some of the basic classes in the game, then the game trying to load an old save file based on the previous version of the classes.
If you have an old save file, I'd recommend deleting it - go to C:\Users\YOUR_USER_NAME\AppData\LocalLow\Satisficing Itch\Battle Succubi and delete the file Game.dat and see if that works.