Wikipedia
The or the Great Council of State was (i) (Daijō-kan) the highest organ of Japan's pre-modern Imperial government under 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.
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).
The Imperial governing structure was headed by the Daijō-kan. This council and its subsidiary ministries handled all secular administrative affairs of the country, while the Jingi-kan or Department of Worship, oversaw all matters regarding Shintō ritual, clergy, and shrines.
This structured organization gradually lost power over the course of the 10th and 11th centuries, as the Fujiwara clan, dominating the post of Imperial regent, began to dominate the Daijō-kan as well. It became increasingly common for the regent to hold the post of chancellor or other office simultaneously. By the 12th century, the council was essentially powerless as a separate entity, though it seems clear that the system was never formally dismantled. Over the course of centuries, the ritsuryō state produced more and more information which was carefully archived; however, with the passage of time in the Heian period, ritsuryō institutions evolved into a political and cultural system without feedback.
By the time of Emperor Kōmei, the kuge aristocracy were joined in common goals by a number of newly powerful provincial figures from outside Kyoto. Together, this tenuous, undefined coalition of men worked together to restore the long latent prestige, persuasive power, and active strengths of a re-invigorated Imperial center. This combination of factors thrust an archaic hierarchy into the center of national attention, but with so many other high-priority matters demanding immediate attention, there was little time or energy to invest in reforming or re-organizing the Daijō-kan.