Female-line Emperor (女系天皇)
The term "Female-line Emperor" (Jokei Tenno) refers to an Emperor of Japan who is a descendent of the imperial line only on his/her mother's side; such an emperor may also be referred to as a `Mother-line Emperor.'
In fact, no Emperor has ever ascended the throne for this reason alone.
Since the Japanese terms for "Female-line Emperor" (女系天皇) and "Female Emperor" (女性天皇) are somewhat similar in wording, the meaning of "Female-line Emperor" is often confused with that of "Female Emperor;" given that the term "Female-line Emperor" is related to imperial bloodline while the term "Female Emperor" is related to gender, their concepts are quite different. Regardless of the gender of the Emperor, both female-line male Emperor and female-line female Emperor can conceptually exist.
According to the statements in the "Kojiki" (Records of Ancient Matters), "Nihonshoki" (Chronicles of Japan), and other history books, the Japanese imperial line has been succeeded by the male bloodline since the first Emperor Jinmu to the hundered and twenty-fifth present Emperor (so-called `unbroken line of Emperors,' however, there are many views regarding the credibility of this theory including the view of Itsue TAKAMURE; that imperial succession was based on the mother-line in ancient times.)
From the perspective of an unbroken line of Emperors, a Female-line Emperor doesn't belong to the imperial lineage originating from Emperor Jinmu even if he/she ascended to the throne, therefore, leading to the first-ever dynastic change in Japan.
The regulation that `only male-line descendants of the Emperor are able to succeed the imperial throne' was established in the Meiji era; 1868 - 1912 based on the former process of imperial succession.
It is usually assumed that eight female Emperors in ten generations, including six female Emperors in eight generations during the period between the end of the sixth century and the latter half of the eighth century, were in the past, and it is undeniable that their father was either Emperor or Crown Prince. It is also assumed that they are either unmarried (for their entire lifetime) or formerly-married to an Emperor or a Crown Prince (widow, not remarried) (refer to Family Tree below). At that time, a female member of Imperial Family must abandon their membership in the imperial family if she marries a non-imperial family member, therefore her child never succeeds the throne. It is uncertain whether a child between a female member of the Imperial Family and a male member of a non-Imperial Family member obtains the right to succeed the throne or not; the person whose mother is a member of the Imperial Family was regarded nobler than their general peers, so called `Miyahara' (born to a female member of the Imperial Family). There is a theory that a few alternations or falsifications were made to the genealogy during the periods of Kinmei, Suiko, Saimei, and therefore careful examination is required.
As for the imperial line before that period, Nakatsusumeramikoto ron; if the existence of Empress or Princess who was a liaison between God and Emperor advocated by Nobuo ORIGUCHI, is considered, female-line Emperors might have existed (some people say that they were neither female-line nor male-line but female & male-line Emperors).
Before Meiji Period; Empress Jingu who played a role as Emperor during the period when no Emperor reigned was regarded as Emperor. There is also a view that female imperial family members such as Princess Iitoyo or Kasuga no Yamada no Himemiko (Princess) were Emperors because they played a role for political reasons. Furthermore, there is an opinion that quite a few inconsistencies in "Kojiki" and "Nihonshoki" are solved, and deceased persons in the gigantic ancient tomb are easily identified by reviewing history adopting the Nobuo ORIGUCHI's theory regarding Nakatsusumeramikoto; Empress or Princess who is a liaison between God and Emperor, and the Hime-Hiko system advocated by folklore scholars; the Princess-Prince system; governing the country by female and male imperial family members.
There are some cases such as the thirty-eighth Emperor Tenji, the fortieth Emperor Tenmu, or the forty-second Emperor Monmu who was the child of a Female Emperor and succeeded the throne; their father (the husband of the Female Emperor) was also Emperor or Prince (Refer to Family Tree below). In addition, according to the age of Tenmu stated in "Ichidaiyoki" (summary chronicle of each reign) in the Kamakura period and "Honcho Koin Joun roku" (the Emperor's family tree) in the period of the Northern and Southern Courts, Tenmu was four years older than Tenji, for which some scholars including Katsuaki SASA, Keiko KOBAYASHI, and Iwao OWA advocate a tentative theory that the father of the fortieth Emperor Tenmu was not the thirty-fourth Emperor Jomei, and it is also advocated that the prerequisite for succeeding to the throne was that his mother was the thirty-seventh Emperor Saimei no matter who his father was; anyway, this is a tentative non-official theory and not accepted by the historical community. If we rely on this theory, the thirty-eighth Emperor Tenji and others were also regarded as Female-line Emperor rather than Male-line Emperor based on the genealogy. Various falsifications seemed to be made in the "Kojiki" and the "Nihonshoki," and one of the problems arising from the falsifications is that the imperial line was indicated as if it had been succeeded by Male-line Emperors. In ancient times, belonging to a clan was based on the father-line, but customs are based upon the mother-line, therefore it is suspicious that the succession of a household was always based on the father-line (In subsequent periods, there has been a system taking a son-in-law into the house).
In Japan today, a married couple chooses a husband/wife's surname for them and their child in accordance with the Civil Code, and most married couples chose the surname of the husband/father. Supposing that the succession of the surname represents the succession of the household, it can be said that male-line succession is common in the nation, however, a few son-in-laws or daughters take over the family; a remaining convention from the past female-line succession.
Male-line male `married into' Imperial female family
In the past, there were at least three cases where a male-line male might have been `married into' an Imperial female family.
The first case is the twenty-sixth Emperor Keitai (according to the Kojiki (Records of Ancient Matters) and the Nihonshoki (Chronicles of Japan)) who was supposed to be a descendant from five generations (grandson of great-grandson) of Emperor Ojin who lived in Echizen (present-day Fukui Prefecture) or Omi (Shiga Prefecture); there is a theory that he didn't succeed any bloodlines of former Emperors, leading to a dynastic change; however, it was identified that the genealogy, indicating that he was a descendant of Emperor Ojin, no later than the era of Empress Suiko, was handed down through recent research. Refer to Emperor Keitai.), after the death of the twenty-fifth Emperor Buretsu, Emperor Keitai moved from another province and ascended the throne since Emperor Buretsu's direct descendants were all female descendants (no male descendants). At that time, the twenty-sixth Emperor Keitai had an Empress and they had at least two sons who were in line to become the twenty-seventh Emperor Ankan, and the twenty-eighth Emperor Senka, and after the move, he married Princess Tashiraka who was the sister of Emperor Buretsu and ascended the throne, he subsequently had a son who was going to be the twenty-ninth Emperor Kinmei. The two Emperors; Emperor Ankan, Emperor Senka, also married sisters of Emperor Buretsu as well as Emperor Keitai.
The second case is the forty-ninth Emperor Konin who was the male-line grandson of the thirty-eighth Emperor Tenji; his father, Prince Shiki who possessed the right to the imperial throne, was the son of thirty-eighth Emperor Tenji. He married the Imperial Princess Inoe who was a sister of the Female Emperor, the forty-eighth Emperor Shotoku, and who was the Princess of the forty-fifth Emperor Shomu and had Imperial Prince Osabe. The forty-seventh Emperor Junnin, the son of Imperial Prince Toneri (deposed Emperor Awaji) who was given the throne from the forty-sixth Emperor Koken (the second accession by Emperor Shotoku) after his abdication of the throne, he did not marry a female member of the Imperial Family. The Emperor Junnin was overthrown by the Retired Emperor Koken, and Retired Emperor Koken ascended the imperial throne for the second time as Emperor Shotoku, and he passed away being single. When the direct male descendant of Emperor Tenmu was not available, Emperor Konin, the direct male descendant of Emperor Tenji, was a back up, and the Imperial Prince Osabe became prince even though he was young. Soon after Imperial Prince Osabe was overthrown following his mother, Imperial Princess Inoe, who was overthrown in a rebellion, and Kanmu, born to Emperor Konin and Niikasa TAKANO, the daughter of the descendant of the Paekche Royal Family, became the fiftieth Emperor.
The third case; the hundred and nineteenth Emperor Kokaku. Since there was no son when the hundred and eighteenth Emperor Gomomozono in direct line passed away, Emperor Kokaku, the sixth Prince of Imperial Prince Kanin no Miya Sukehito, became the adopted child of Emperor Gomomozono and ascended the imperial throne with Imperial Princess Yoshiko, the only princess of Emperor Gomomozono. However, the Imperial Prince and Princess of Imperial Princess Yoshiko died early in life, and did not ascend to the imperial throne.
Uncertainty regarding the continuity of male-line
It is assumed that the imperial line is an unbroken line and there is uncertainty regarding it. There are some theories including: the bloodline died out in the era of the twenty-sixth Emperor Keitai; the line was broken at the time during the Jinshin War or during the period of the Northern and Southern Courts. Based on these theories, it is advocated that the imperial line is not an unbroken line of male-line. For further information, refer to the section on Unbroken Line.
Precedent of Female-line Emperor
From the perspective of the `Female-line' theory, the forty-fourth Emperor Gensho was given the imperial throne by his mother, the forty-third Emperor Genmei who was the Emperor at the time. The theory is that his father, Prince Kusakabe didn't ascend the imperial throne although he was a Prince, which means he succeeded to the imperial throne from his mother; the Emperor, leading to the theory; Emperor Gensho is a Female-line Emperor. Besides, tracing back the male-line, Emperor Gensho is an imperial family member descending three generations from Emperor Tenmu, he was regarded as the Imperial Prince before his accession to the throne due to his bloodline from his mother, Emperor Genmei.
It is certain that Emperor Gensho is a Female-line Emperor having his mother as Emperor as well as being a Male-line Emperor that can be traced back to his father, therefore; he is a Female & Male-line Emperor. This concept applies to various Emperors regarded as Male-line Emperors.
There is a theory that the succession of Emperor Gensho was based upon the condition of the accession of young Prince Obito, who was going to be Emperor Shomu; the Prince of the forty-second Emperor Monmu. Another theory denies the theory that `Emperor Gensho ascended as a relay because the Prince Obito was only fourteen years old at the time Emperor Gensho ascended to the throne. (There is a theory that the issues of the imperial court at that time; including issues concerning Prince Nagaya or FUJIWARA no Fuhito, didn't allow the prince Obito to ascend to the throne considering his age). Also, Emperor Gensho ascended to the throne as a child of his father, Prince Kusakabe, not as a child of his mother, Emperor Genmei, however, Prince Kusakabe himself was also Male & Female-line Emperor having Emperor Tenmu for his father and Emperor Jito for his mother.
Regarding this issue, from the perspective of the `Male-line' theory, he was not a Female-line Emperor since his father, Prince Kusakabe was a male imperial family member with male-lineage belonging to the imperial line, and Emperor Gensho's accession to the Imperial throne resulted from the fact that his father was an imperial family member regardless of his mother, Emperor Genmei, being the Emperor. In fact, Emperor Gensho ascended to the throne as a child of Prince Kusakabe and not as a child of Emperor Genmei, his mother. The succession to Emperor Gensho was based on the condition of the accession of young Prince Obito (the Prince of Emperor Shomu and the forty-second Emperor Monmu; he became a Prince during the era of Emperor Genmei) to the imperial throne.
In addition, there is an opinion that based on the precedent of Emperor Genmei, the male-line is maintained even if a female member of Imperial Family ascends to the throne as long as her husband is an old imperial family member from the imperial male-line.
Origin of Male-line Principle
It is uncertain as to when and how the unwritten rule limiting succession to the imperial throne to male imperial family members was established.
According to the Kojiki and the Nihonshoki or other history books about Emperors, the reply to the question `Why should it be male-line?' is always `Because it should be.'
The paternalistic clanship under which a daughter is not allowed to succeed the household, originating in China, introduced from Korea, may have helped to establish such an unwritten rule, but that is not all about this. There is a little difference between China and Korea as well as between Japan and China: None of male-line Female Emperors or kings appeared in successive dynasties in China (Busokuten was the Emperor of the new dynasty for only one generation); Three male-line female Emperors ascended to the throne in Silla, Korea.
In the old Imperial Family Law, the principle of male-line succession was established as a written law, and the current Imperial Family Law also followed it; the official interpretation of it by the government doesn't exist before/after War.
"Koshitsutenpan gige," the official clause-by-clause descriptions, just states the Male-line Succession Provision in Article 1 of the old Imperial Family Law was defined pursuant to `Established Law of Imperial Family,' `Unchangeable unwritten law.'
However, like most other dynasties, the Japanese imperial line also has faced succession crisis due to the shortage of male imperial family members from time to time. Sometimes, accepting female-line, rather than sticking to male-line succession, was much easier; the imperial court or Bakufu (Japanese feudal government) chose to maintain male-line succession.
The reason for that choice can be found in "Tenjo Mukyu no Shinchoku" (God's prophecy in eternal heaven and on earth) in the Kojiki, the Nihonshoki and mythology.
It is the recognition that `Male-line succession is a commandment which has been defined since before the first Emperor Jinmu, and it is a consistently succeeded tradition.'
Therefore, it can be led to a mythological reason such as `The Female-line Emperor who doesn't belong to the unbroken imperial line is not accepted by Koso Koso (Amaterasu - the sun goddess) or the spirit of imperial ancestors).
From such perspective, some male-line advocates claim the female-line acceptance theory is a stepping stone for emperor system abolition and criticize them. In fact, this cannot be denied; in case that the Female-line Emperor is approved, dynasty changes one after another, prescribed earlier in accordance with the principle; dynasty change in male-line succession, and the relationship with present imperial household is getting thinner year by year.
Difference from European Royal Household
The European Royal Household differs from Japanese Imperial Household in historical backgrounds, etc., and their differences are shown below.
In many countries in Europe before, the imperial throne was succeeded by male-line male (different from that of Japan excluding male-line female). This is because the provision in Lex salica, or tribal law that is affected by Lex salica, that land is succeeded by only the male was used as an Act of Settlement. Since countries where Christianity is believed have a monogynous system, a female-line royal family member often ascended to the throne and started a dynasty due to the discontinuity of male-line. Therefore, dynasties like the imperial household in Japan whose line can be unfailingly traced back in the genealogy, at least 1,500 years, doesn't exist in Europe except for the Capetian Dynasty male-line family that governed France for about 800 years, and governs Spain even now.
In Europe, regardless of male-line or female-line, only children who were born between royal families (including royal family members from other countries and prosperous peerage) have been allowed to ascend to the throne. There is a theory that Royal Families are connected by blood even if his/her father is a royal family member from another country; international marriage between Royal Families was common, for that reason, female-line dynasty change was smooth. On the other hand, in the Japanese Imperial Household in ancient times, the child of an Imperial family member father was allowed to succeed the throne; many children who were born between the male Imperial Family Members and the female subjects ascended to the throne. In an extreme case, the mother of the hundred and nineteenth Emperor Kokaku was a commoner. This was not very common in European Royal Households where they were very strict about marriage with a commoner.
Some people say that it is only the Japanese Imperial Household that regarded their ancestors as mythological characters; in ancient Europe, there were Royal Families that also regarded their ancestors as deities of Greek Mythology or Scandinavian Mythology. There are not such Royal Families now because some died out or some let go of their mythologies converting to Christianity, not an unusual transformation for the Imperial Family Household.
After the latter half of the twentieth century, a male-line female or a female-line male/female (his/her father can be a subject) is entitled to succeed the throne in most European monarchies; such reform was carried out for `Equality of the Sexes,' so, not always connected to shortage of male-line male. However, in some countries, if the children for succession are an elder sister and a younger brother, the right to succeed the throne is granted to the brother.
As an example, in the British Imperial Household, the eldest son in the direct line is preceded in order of succession; Duke of York, the third child of Queen Elizabeth has a higher priority than Princess Ann, the second child of Queen Elizabeth in order of succession; Duke of York is the forth in line to the imperial throne while Queen Ann is the tenth having a lower priority than her younger brothers and their families
Modern Imperial Household and Female-line Emperor
In the Imperial Household, there was a concern for forty one years that the imperial line would die out; from when Akishinonomiya Imperial Prince Fumihito was born in 1965 to when Imperial Prince Hisahito was born in 2006. Therefore, there was an opinion that female-line succession should be approved by revising the principle of succession, however, there is still time to consider such issue. Both male-line and female-line advocates agree that discussions regarding the imperial succession issue and imperial family should continue.
Imperial Princess Aiko of the Crown Prince's Household and Imperial Princess Mako and Yoshiko are male-line imperial female members that could become Emperor candidates by tracing only their father's line. However, if they marry commoners in future and have children, their children can not become Emperor candidates regardless of their sex, thus they will be determined as female-line (refer to Family tree below).