Two things: a) does anyone else get a Mighty Whitey vibe from the implication that Western medicine may be the key to eradicating the Redface Pox?
The vaccine was discovered and experimented by japanese so at the end the answer could be a no.
And b) if they get to Shogun Ienari, how the hell are they going to do the gender flip? The real Ienari was said to have fathered 75 children, how are they going to reconcile that with a female shogun? They're either going to have to severely reduce the number of children down to the direct heirs and key players or make Ienari the first male shogun in decades. (Yes, I have been reading about the shoguns on The Other Wiki, why do you ask?)
I may have figured this out. Of course Ienari will be the first male shogun in decades. The Redface Pox will be eradicated by then, if one WMG is correct.
Well, it's not completely eradicated but Ienari is indeed the first male shogun.
Why do they still need a shogun? It's repeatedly noted that with men in short supply, wars are the last thing on anyone's mind, and with it standing armies.
The Emperor had been sidelined almost entirely since the late 1100s. It is not quite at the level of "Why bother with a king, the pope is still there." but it is close.
Actually, that brings up another question: is the Emperor another case of She Is the King? I can't imagine that they managed an unbroken line of male succession, especially if they keep marrying off their princes to the shoguns.
The Imperial throne going matrilineal is actually MORE plausible than the shogunate, given that there had been 6 reigning Empresses by the time the Tokugawas came to power. My guess would be that Ooku-verse Empress Meisho came to the throne after the Redface Pox went through Kyoto, and that female inheritance will continue at least through the reign of Empress Go-Sakuramachi.
We might see some changes soon then, cause Volume 9 ends right in the middle of Go-Sakuramachi's time on the throne.
I just realized a premise-induced plot hole: why did Harusada relinquish her claim to the shogunate? In real life Ienari became shogun because Ieharu had adopted him as his heir, but in the Ookuverse, unless I missed something, the female Ieharu did no such thing. And certainly everyone had expected Harusada to become the next shogun. So why didn't she, other than the need to follow real life history as close as possible (which isn't a reason in universe)?
My assumption was that if she did, they would have expected her to produce a girl heir, and she knew that it was getting more likely that she wouldn't get pregnant again at all, so better to go with the heir she already has. Like she says, there's no fear of Toyochiyo dying of the redface pox, and he can attempt reproduction as often as he likes. Unlike his predecessors, he's not limited by a single wombnote given that so many heirs have died as a result of poor health from birth- although this may also be a problem with the medical knowledge of their time. (And as mentioned far above, he definitely does his darnedest to spread his seed around.)
If they're meant to be the same age as their real life counterparts she would be in her late thirties, so it would be harder for her to produce an heir. This is actually a pretty sound guess.