That means we should be rather cautious when we face an “ancient tradition” that is presented to us in order to justify a solid present-day political agenda.
In fact, there are several historians who contend that the “stop gap” theory concerning Japan´s female tennos does not hold up against the historical facts. (The “stop gap” or “intermediary” theory claims that women only came to ascend the Japanese throne when no male heir could be found or was still minor, which would mean that female tennos only served as a sort of “fill in” for some time until a male heir became of age.)
E. Patricia Tsurumi, Professor emerita of History at the University of Victoria, argues that the intermediary theory does not explain, for example, Empress Gemmei´s transfer of the throne to her daughter, Empress Gensho. When Gemmei abdicated, Crown Prince Obito was, at seventeen, certainly old enough to succeed. Still, Gemmei obviously preferred “her own beautiful, able and energetic daughter of thirty-six years” over Obito as the next monarch. Tsurumi also takes a look at the other reigns of Japan´s six early empresses and comes to the conclusion that “the intermediary theory fits only the case of Kyogoku Saimei perfectly. [Empress Kōgyoku (594–661) reigned a second time as Empress Saimei.] All other fits are imperfect at best, and sometimes they are impossible.“
Hitomi Tonomura, a historian of the premodern period who teaches at the University of Michigan notes that the position of Japan´s ruling empresses “has been misconceived in modern times since the Imperial Household Law of 1889 disqualified women from the throne“. Tonomura reports that “the term excluding women from the imperial office was introduced in the 1889 Imperial Household Law, as Japan sought to reconstitute itself in the West-dominated world order. Thus, the term was less a product of Japanese history than a modern invention that required justification. Historically, eight female emperors occupied ten reigns. Therefore, the adoption of the exclusionary term involved a fierce debate ranging over numerous perspectives and interpretations.” During this debate, Meiji time “modernizers” who wanted to make it impossible for women to henceforth ascend the throne, argued that the Japanese tradition of women rulers had not been very relevant as these empresses had served – according to them – as mere stop gap rulers and had not passed the throne on to their children. On the other hand, Meiji time traditionalists who wanted to keep the tradition of female monarchs, contended that “excluding women from imperial rule not only went against the classical basis of the country, but also greatly injured people’s kokoro (hearts).”
We know that the Meiji time “modernizers” won the day not only insofar as presently, women are in Japan not allowed to ascend the throne but also in that nowadays nearly everybody shares their interpretation concerning the insignificance of Japan´s female tennos. Actually, although it is sometimes claimed today that the problem of conservatives is with a female line, not with a female tenno, it is obvious that there is something wrong in this picture: under the current law it is not only Aiko´s children who will be kept away from the throne, it is Aiko herself.
Professor Tonomura clearly criticizes the attempt to downplay the importance of the historical role of Japan´s eight reigning empresses by asserting that they had been mere “stop-gap” rulers who abdicated once a suitable male heir came of age, because, as she expresses it, “this one-dimensional characterization does not hold up against the evidence”. She states that male candidates were available in most cases when female emperors took office. For example, Suiko, the first of the six ancient female emperors, was enthroned in 592 at 39 years of age. Her nephew, Prince Umayado (later called Shotoku), was 18 when she ascended the throne, a male mature candidate of imperial descent. As Tonomura states: “If gender was the primary factor in the selection of an emperor, the choice of Suiko makes no sense.” Suiko never abdicated (as later Japanese tennos often used to do) and died at the age of 75, after reigning for 36 years.
On the other hand, Tonomura notes that while there were often male heirs available when women took the throne, it also happened in later centuries that at times when there actually was a dearth of male heirs and the installation of an “intermediary” figure would have been useful, no woman was put on the throne. Tonomura explains this on the basis of the social changes that took place in the 7th and 8th centuries. The period of the six early female rulers, “170 years during which women frequently took the helm,” was “the monumental period of Japan’s state-building.” Each reign, whether male or female, “resulted from complex power relations among the members of the imperial and ministerial families.” Royal qualifications “derived just as much from the mother as from the father, and there was no established rule of patrilineal succession before the end of the eighth century.” This reflected the ways of Japan´s contemporary elites, among whom bilateral descent was also the custom at the time.
But after that period, from 770 until 1630, no woman ascended the Chrysanthemum Throne. Tonomura attributes the dearth of female emperors after 770 to “a larger rhythm of social transformation—the diminishment of women’s level of economic and familial independence between 592 and 770. Women became absorbed into male-centered systems of residency, economy, and politics, and ceased to live in their own quarters. Society gradually moved from bilateral descent toward patrilineal descent.” That means that the imperial institution and its rules kept reflecting the changing customs of the society of which it was a part. Female rule “ended as society moved toward increasingly male-centered structures and values, which female emperors themselves had helped to institute.”
If Tonomura is right – and I, for one, find her argumentation very convincing – we could say that, in the past, the Japanese monarchy adjusted to the times and reflected social changes by increasingly insisting on the monarch to be male. But if that is so, it would obviously not break the tradition but rather carry it on if the monarchy in the 21st century also chose to reflect the social changes that have taken place and allow a woman on the throne.
Once more.
- is clearly a legend. Empirical evidence indicates that the monarchy in Japan originated around the fifth century A.D.. Nevertheless, the (still) official genealogy of the imperial house claims that the first tenno, Jimmu, founded the monarchy in 660 B.C. This 660 B.C. date is very obviously made up. The authors of Japan´s first historical records, the “Kojiki” (712 A.D.) and the “Nihongi” (720 A.D.), quite simply used Chinese astrological and genealogical tables, calculating that 1260 lunar years had passed since the reign of the first (Chinese) emperors. (Imperial China was at the time the much-admired great role model of the budding Japanese monarchy.) Taking 600 A.D. as their starting point and subtracting 1260, they concluded that, to be on a par with the Chinese monarchy, the first Japanese emperor ought to have ascended the throne in 660 B.C. So, they just maintained that he had... 
I am not sure if that is comical or rather scary.
) 
If I may quote myself:
