The grandfather of the current emperor, Emperor Taisho, who was sick and mentally weak was the first (in recent times) to not have children by women other than his wife.
He was the son of a “lady-in-waiting” as consorts were called; which if I weren’t the enlightened male of the ‘00s, I would have to say is a cool sounding name – at least for the guys who had them waiting around.
Taisho’s father, the Emperor Meiji, was in turn the son of his father, an emperor and a lady-in-waiting.
Taisho did his duty, though, and produced an heir (Emperor Showa, known as Emperor Hirohito outside of Japan) and not just one but three spares. Unfortunately, Hirohito was only able to barely manage the heir and spare requirement, but was handicapped by the disqualification of his five daughters. In the meanwhile, Hirohito’s brothers fell down on their duties and only one of them produced males, none of whom continued producing possible successors.
The current Emperor has two sons, but as noted above, the oldest son, and Crown Prince has only one daughter (widely believed by people outside of Japan to be done in vitro) and between Masako’s (the Crown Princess) infertility and mental breakdowns, it was impossible to get any more children.
Akishino, the second son had had two daughters, and was seemingly content to stop there, but it’s thought that the Imperial Household Agency put more pressure on them to continue until they had a son. (There’s a gap in ages between the two daughters and the son, with his daughters born in ‘91 and ‘94, and then his son in ’06.)
Unfortunately, Japan doesn’t discuss these things openly so there’s little printed material to go on. They even claimed that even the doctors had no idea if the child was going to be a son or daughter until the birth, which in these days, seems “unlikely” as my wife’s ob/gyn agrees.
Back to the question of “ladies-in-waiting,” one of the older princes gave that as a suggestion of how to handle the succession crisis.
