I think it's hit the enemy with the bat 8 times? Not sure myself, I managed to get it once on normal. There's also some medal you can colect with a purple girl inside the boxes for each level, though 1-3 doesn't seem to have one. I really hope the developer creates better resolution options and a mouse lock so I don't go out of screen all the time. And a zoom in feature for these animations with darker backgrounds, or a gallery should suffice.
You can get 1000 points for beating normal and 3000 points for beating hard, the chained succubus is pretty badass but a maxed out normal succubi is actually stronger with all the skills she has in the demo. It's really easy to find the cheat engine parameter for points if you have around 1000 points. Finally, the save file is created in your Appdata/Locallow/default company folder.
There's a few bugs by the way in this new demo; one with the chained Succubus in her reverse cowgirl pose if she makes a guy climax twice she'll enter a state where she's frozen with the enemy. Also some of the Story cut-scenes might not load, not sure what causes it but if you reload the game it'll act like you already saw the cut-in. You can replay it talking to the yellow haired succubus menu.