Consider this a bug testing report regarding all the crashes. I was experiencing a crash every time I finished the monster nest event in the last stage, regardless of what scene (white, black, or big succubus) preceded it. Unlike the other crashes, this one seemed to happen all the time, rather than being partially random.
I completed the game and came back to this, but no change.
I found I could escape from the succubi, rather than going to the nest, without a crash, so it was definitely something to do with the nest.
I eventually got it not to crash. Two factors were different compared to the previous attempts.
1) I skipped the succubi event for being dropped to 0 health and went straight to the nest. Since I had just tested if escaping from the succubi worked, I now had the option, and given what people said about being caught by a monster girl fixing the crashed for returning home, I thought maybe there was something going on with the scene.
2) I turned my BGM and SE all the way down, because in other MTL games I've tried in the past, there have been issues caused by the game trying to find music or a sound but not being able to due to something being wrong with the translation.
Either of these could have been the fix for the crash. I don't know witch, but I hope this is helpful for making a more stable version of the game later.