John wrote:...?!!..??!...
Aren't YOU the inquisitive one today!? (Touché to you!)
...alright,... workin' on it.
<pause>
OK,.. how's this "sketch" of a hypothesis...
In "good times" (definition?) women get "crazy" (definition?) and "drive" (definition?) men of reproducing age and inclination "away" (definition?) and don't reproduce as "necessary" (definition?).
When societies "stabilize" (definition?) women have "better things to do" (definition?) than birthin' babies, thereby making them "crazy" (see definition above, when supplied).
Once again, it's "all" (definition?) women's "fault" (definition?). And that may not be an unnatural bad thing.
Personally, I think it's the insular (isolationist island) nature and homogeneity of Japan that "masks" the actual mechanism of the "mystery of the missing war(s) fatalities".
"Diversity" (non-uniformity) may be the "hated thing" that drove, and drives, the "killing" of the "excess" population during those (these) GD Genocidal Crisis war periods. Those who "can't fit in", or are simply not allowed to do so, aren't allowed to reproduce, and those who refuse to limit their reproduction who are "unfit" are declared criminals and exterminated along with their "unauthorized" offspring.
So, it's either self-prune that part of the national population tree that you personally control, or some other "force" will do it for you.
Assuming it's true that Japanese are not treated well, as a group, by their husbands, it seems to me that the women either know or intuit that their job is to protect their family from the "societal katana" that will annihilate their line if they "overproduce" (thus becoming a societal disturbance by creating jealousy), even if that means putting up with frustrated husbands who become abusive due to their "sexual frustrations".
...I may expand on this, but I have to get some milk from the store at the moment, so...

Aloha gangies!