"Chunagon" (vice-councilor of state) is a post ranking below Dainagon (chief councilor of state) in the Daijokan (Grand Council of State), the highest organ in the Imperial Court, and is Ryoge no kan (class outside of the Ritsuryo system), corresponding to Suke (assistant director) in the Shitokan (four classifications of bureaucrats' ranks). Its corresponding Chinese names are Komon, Komon jiro, Monka jiro, Shiko, etc. The kani soto (corresponding relationship between court ranks of government officials and government posts) changed from Shoshiinojo (Senior Fourth Rank, Upper Grade) to Jusanmi (Junior Third Rank).
Since many heads of the Mito Clan were assigned as Gonchunagon (provisional vice-council of state), it was referred to as 'Mito Komon.'
The most famous is Mitsukuni TOKUGAWA, the second head of the clan, and 'Mito Komon' generally refers to Mitsukuni.
However, Mitsukuni was Sangi (Royal advisor) when he was the head of the clan, and became Gonchunagon after retirement.
It was abolished on March 21, 701 (old calendar), when Taiho Ritsuryo (Taiho Code) was enforced, but was restored as Ryoge no kan on April 17, 705 (old calendar). At the time, the kani soto was Shoshiinojo. The main function was to fill in for the Dainagon, present imperial letters to the emperor, wait for inquiries, and to attend conferences at the Daijokan, much the same as Dainagon, but unlike Dainagon, they could not act on behalf of the minister. The number of regular personnel was originally three. On February 1, 761 (old calendar), the kani soto was revised to Jusanmi, since the salary was low despite heavy responsibilities. Later, the number of personnel assigned varied with time, and reached ten when highest, but was fixed at eight during the reign of Emperor Gotoba.
According to the "Kanshoku konan" ("官職今案") by Tomokiyo TAKADA, during the period of the Northern and Southern Courts (Japan), as with Dainagon, there were only temporary personnel and official personnel were nonexistent.
The basic condition to be assigned as Chunagon is to have experience serving one of the following posts.SangiSadaiben/Udaiben (major controller of the left/right)Sakone no chujo/Ukone no chujo (Middle Captain of the Left/Right Division of Inner Palace Guards)Kebiishi no betto (Superintendent of the Imperial Police)
Additionally, it was customary for the sons of Sekke (line of regents and advisers) to be assigned as Chunagon from Chujo (Middle Captain) without experiencing Sangi.