Sadaijin in the context of "Taihō Code"

The Daijō-kan or Dajō-kan (Japanese: 太政官), also known as the Great Council of State, was (i) (Daijō-kan) the highest organ of Japan's premodern Imperial government under the Ritsuryō legal system during and after the Nara period or (ii) (Dajō-kan) the highest organ of Japan's government briefly restored to power after the Meiji Restoration, which was replaced by the Cabinet. In Yamato name it is also called "Ōmatsurigoto-no-Tsukasa" 於保伊萬豆利古止乃官）.

It was consolidated in the Taihō Code of 702. The Asuka Kiyomihara Code of 689 marks the initial appearance of this central administrative body composed of the three ministers—the Daijō-daijin (Chancellor), the Sadaijin (Minister of the Left) and the Udaijin (Minister of the Right).

Minister of the Right (右大臣, Udaijin) was a government position in Japan during the Asuka to Meiji era. The position was consolidated in the Taihō Code of 701. The Asuka Kiyomihara Code of 689 marks the initial appearance of the Udaijin in the context of a central administrative body called the Daijō-kan (Council of State). This early Daijō-kan was composed of the three ministers—the Daijō-daijin (Chancellor), the Sadaijin (Minister of the Left) and the Udaijin. The Udaijin was the Junior Minister of State, overseeing all branches of the Daijō-kan. He would be the deputy of the Sadaijin.

From the Kamakura period (1185–1333), when the warrior class came to power in Japan, this imperial court position became an honorary position with no real authority. Oda Nobunaga, who was a powerful daimyo in the Azuchi-Momoyama period, was a daimyo who held this imperial court position. This was the first time since Minamoto no Sanetomo in 1218 that a member of the warrior class had been appointed Udaijin. Previously, the only warrior class members appointed to higher positions than Udaijin were Taira no Kiyomori and Ashikaga Yoshimitsu as Daijō-daijin, and Ashikaga Yoshinori and Ashikaga Yoshimasa as Sadaijin. The warrior class was able to use the high imperial court positions of Daijō-daijin, Sadaijin, and Udaijin, which had originally belonged to the nobility, as a means of establishing their own authority.

The Tachibana clan (橘氏, Tachibana-uji, Tachibana-shi) was one of the four most powerful court nobility (kizoku or kuge) families in Japan's Nara and early Heian periods—the other three were the Minamoto, the Fujiwara, and the Taira. Members of the Tachibana family often held high court posts within the Daijō-kan (Ministry of State), most frequently Sadaijin (Minister of the Left). Like the other major families at court, they also constantly sought to increase and secure their power by marrying into the imperial family. However, as the Minamoto clan and the Fujiwara clan gained power over the course of the 9th and 10th centuries, the Tachibana were eclipsed and eventually became scattered across the country. Though serving in high government posts outside the capital, they were thus denied the degree of power and influence within the court at Kyoto (Heian-kyō) which they once enjoyed.

The name of Tachibana was bestowed on Agata-no-Inukai no Michiyo by Empress Genmei in 708. She was the wife of Prince Minu, a descendant of Emperor Bidatsu and mothered Princes Katsuragi and Sai. She later married Fujiwara no Fuhito and bore Kōmyōshi (Empress Kōmyō). In 736, Princes Katsuragi and Sai were given the surname Tachibana, renouncing their imperial family membership. They became Tachibana no Moroe and Tachibana no Sai respectively.

The Asuka Kiyomihara Code (飛鳥浄御原令, Asuka Kiyomihara-ryō) refers to a collection of governing rules compiled and promulgated in 689, one of the first, if not the first collection of Ritsuryō laws in classical Japan. This also marks the initial appearance of the central administrative body called the Daijō-kan (Council of State) composed of the three ministers—the Daijō-daijin (Chancellor), the Sadaijin (Minister of the Left) and the Udaijin (Minister of the Right).

In 662, Emperor Tenji is said to have compiled the first Japanese legal code known to modern historians. The Ōmi-ryō, consisting of 22 volumes, was promulgated in the last year of Tenji's reign. This legal codification is no longer extant, but it is said to have been refined in what is known as the Asuka Kiyomihara ritsu-ryō of 689. The compilation was commenced in 681 under Emperor Tenmu. The Emperor died in 686, but the finalization of the Code took a few more years. It was promulgated in 689. These are understood to have been a forerunner of the Taihō ritsu-ryō of 701.

Tachibana no Naramaro (橘奈良麻呂; 721–757) was a Japanese aristocrat (kuge), courtier, and statesman of the Nara period. He was the son of sadaijin Tachibana no Moroe and the second head of the Tachibana clan. He attained the court rank of shō shi-i no ge (正四位下) and the position of sangi, and posthumously of shō ichi-i (正一位) and daijō-daijin.

He was the leader of a plot to replace Fujiwara no Nakamaro and to overthrow Empress Kōken (Tachibana no Naramaro's Conspiracy). It was not successful.