Securing an heir through ”Ryoto Tetsuritu system" (the heir is alternately chosen between 2 lines)

Whether you're a king, a general, or a company owner, it's human nature to want to choose your heir from among your children. The imperial line is no exception; siblings or direct descendants are considered as successors, but as the order of succession is not defined, the selection process is arbitrary and political. In the samurai government, for example, the Tokugawa family prepared family ranks such as Gosanke and Gosankyo to secure a spare successor to the Shogunate based on past failures, and the Shibukawa family and Kira family are said to be equivalent to such Gosanke. In order to protect the one lineage that lasts forever, it was necessary to always have a certain number of candidates for the male heir, and by the beginning of the early modern period, the imperial family had established a system of hereditary imperial families, but until then, there was a question of how much of the imperial family should remain (If there are many, to what extent should they be lowered from subject status?) and it was an important issue whether who should be declared imperial princes. The status of the Miya-ke and Gosanke is inherited even if they are distantly related to the head family, but if you want to ensure a certain pool of successors and have your descendants inherit the position, Ryoto Tetsuritsu might makes sense, however, as long as the relationship between the siblings' families is good.

In the first place, the premise of the Nanbokucho was the "ryoto tetsuritsu" (heirs were appointed alternately from the descendants of each family). It all started when the younger brother (Emperor Kameyama) became more attractive than the elder borother (Emperor Gohukakusa) for their father (Emperor Gosaga) and the Emperor Gohukasusa abdicated the throne, but after that, these two lines fought over succession for about 150 years. Although the Imperial Court at the time was effectively losing its right to govern Japan, in the first half of the Kamakura period, the Imperial Family still held vast manor territories and was an important as "private ruler." Emperor Gofukakusa's lineage is called the Jimyoin line (Northern Court), and Emperor Kameyama's lineage is called the Daikakuji line (Southern Court), but each inherited a huge group of manors called Chokodo domain and Hachijoin domain, and had a strong economic base. As a result, the Kamakura shogunate tolerated this situation and did not take any strong initiative for succession to the Imperial Throne, which led to a long period of division among the court nobles and samurai families.

Emperor Go-Daigo of the Daikakuji line tried to end this dual state of authority in his generation. The imperial lineage passed down from his father (Retired Emperor Go uda) to his older brother (Emperor Go Nijo) was supposed to be passed on to his son (Imperial Prince Kuniyoshi), but because he was still young, at Emperor Go uda's request, Emperor Go-Daigo named Prince Kuniyoshi as Crown Prince and ascended the throne as short relief. He was extremely dissatisfied with this treatment and attempted to overthrow the Shogunate shortly after his father's death (Shochu Incident, Motohiro Incident), causing the Kamakura Shogunate to collapse sooner than expected. Originally, the issue of imperial succession within the Daikakuji line was shifted to the issue of ``restoration of power by the imperial court'' due to the emergence of the strong individuality of Emperor Go-Daigo, leading to the end of the Ryōtō tetsuritsu, the change of samurai government, and the emergence of the Nanbokucho era. However, as a result, the authority and economic base of the imperial court and court nobles were greatly damaged, and the era of Yoshimitsu Ashikaga entered.  

The Ryoto tetsuritsu was also the Sekkan period, and after Emperor Murakami, heirs were installed alternately in the elder line (Emperor Reizei) and the younger line (Emperor Enyu). Aiming to become the next regent and Kanpaku, Kaneie and his children (Michitaka, Michikane, and Michinaga) tried to maintain their status as the emperor's maternal relative by sending their daughters to both lines as the middle court. In "Hikaru Kimi e" this time (the last week of January 2024), Emperor Enyu abdicates the throne to Emperor Kazan, the throne is transferred from the younger brother line to the older brother line, and Enyu's son (Emperor Ichijo) becomes the crown prince. The back-and-forth relationship between the regents, who would lose their power base if a prince was not born, and the emperor, whose politics would be hindered without the support of high-ranking court nobles, reached its peak during the eras of Michinaga and Yorimichi.

The authority and economic power of the Sekkan family later entered the Insei era, split into five Sekke families, and relatively declined under the samurai government, but while their ability to take ownership as rulers of the Imperial Court diminished, the status of the noble family, which determined how great they could become, became fixed, and was even protected during the Edo period until the Meiji Restoration. In our country, any serious revolution had never occured, and the old / former rulers were protected to a certain degree of honor and economic power, and after the Meiji Restoration, the lord of the Shimazu domain, the Tokugawa head family, the last shogun, and the head of the each Gosekke family became dukes. This is a very Japanese way of doing things, but thanks to the efforts of many people, many relics such as old shrines and temples, ruins, books, and paintings remain, allowing us to visually enjoy the footprints of our predecessors in the past.  

Emperor Kanmu's sons (Emperor Heijo, Emperor Saga, and Emperor Junna) also had the opportunity to be separated among their brothers and their children, but Emperor Saga's lineage eventually continued the imperial line. If we go back further and look at the competing cases of the Tenchi and Tenmu lines, we can see that succession between brothers is particularly prone to trouble in the long-term continuity of the imperial lineage, and I think it will be helpful to modern people as well. Come to think of it, the Arab royal family is basically based on sibling inheritance and a lifetime system, so it is easy to stay within the same generation, and during that time, many successor candidates have been born, so it seems difficult to name a successor. Siblings could be both spares for successors and greatest rivals, so such Ryoto-Tetsuritu system may have been a Japanese solution.