Seishitsu is the Japanese

Japanese language

is a language spoken by over 130 million people in Japan and in Japanese emigrant communities. It is a member of the Japonic language family, which has a number of proposed relationships with other languages, none of which has gained wide acceptance among historical linguists .Japanese is an...

 term of the Edo period

Edo period

The , or , is a division of Japanese history which was ruled by the shoguns of the Tokugawa family, running from 1603 to 1868. The political entity of this period was the Tokugawa shogunate....

 for the official wife

Wife

A wife is a female partner in a marriage. The rights and obligations of the wife regarding her spouse and others, and her status in the community and in law, varies between cultures and has varied over time.-Origin and etymology:...

 of high-ranking persons. The tennō

Emperor of Japan

The Emperor of Japan is, according to the 1947 Constitution of Japan, "the symbol of the state and of the unity of the people." He is a ceremonial figurehead under a form of constitutional monarchy and is head of the Japanese Imperial Family with functions as head of state. He is also the highest...

, kugyō

Kugyo

is the collective term for the very few most powerful men attached to the court of the Emperor of Japan in pre-Meiji eras. The kugyō was broadly divided into two groups: the , comprising the Chancellor of the Realm, the Minister of the Left, and the Minister of the Right; and the , comprising the...

 (court officials), shogun

Shogun

A was one of the hereditary military dictators of Japan from 1192 to 1867. In this period, the shoguns, or their shikken regents , were the de facto rulers of Japan though they were nominally appointed by the emperor...

 and daimyo

Daimyo

is a generic term referring to the powerful territorial lords in pre-modern Japan who ruled most of the country from their vast, hereditary land holdings...

 often had several wives to ensure the birth of an heir. The seishitsu had a status above other wives, called sokushitsu (側室, concubine

Concubinage

Concubinage is the state of a woman or man in an ongoing, usually matrimonially oriented, relationship with somebody to whom they cannot be married, often because of a difference in social status or economic condition.-Concubinage:...

).

The system dates back to the ritsuryō

Ritsuryo

is the historical law system based on the philosophies of Confucianism and Chinese Legalism in Japan. The political system in accord to Ritsuryō is called "Ritsuryō-sei"...

 system in the Nara

Nara period

The of the history of Japan covers the years from AD 710 to 794. Empress Gemmei established the capital of Heijō-kyō . Except for 5 years , when the capital was briefly moved again, it remained the capital of Japanese civilization until Emperor Kammu established a new capital, Nagaoka-kyō, in 784...

 and Heian period

Heian period

The is the last division of classical Japanese history, running from 794 to 1185. The period is named after the capital city of Heian-kyō, or modern Kyōto. It is the period in Japanese history when Buddhism, Taoism and other Chinese influences were at their height...

s. At the time, the main wife was called chakusai (嫡妻). The last Japanese emperor to have official concubines was Emperor Meiji

Emperor Meiji

The or was the 122nd emperor of Japan according to the traditional order of succession, reigning from 3 February 1867 until his death...

.

Succession disputes between sons of the official wife and concubines were a constant source of internal, often armed conflict within houses (O-Ie Sōdō

O-Ie Sodo

O-Ie Sōdō were noble family disputes within the samurai and aristocratic classes of Japan, particularly during the early Edo period...

).