Japanese procreation propaganda at it's finest and I love it.
Basically, women die at 20 if they are still a virgin, and it appears that they can still die even if they lost their virginity if they masturbated too much before losing their virginity. All the women appear to be "manufactured" in some way, it hasn't explained yet. Their genes appear to have been edited so that they are cock craving nymphos. It has also hinted that there is time traveling involved.
The conflict appears to be some women (the eternal roastie) have seemingly killed all men for making "perfect women". While those women are trying to destroy a system they are trapped in as well as they are contained in areas by literal rapists that cum "poison" that causes the women to die.