Omi (臣) was an ancient Japanese hereditary title denoting rank and political standing (a kabane) that, along with muraji, was reserved for the most powerful clans during the Kofun period. The omi clans generally took their names from the geographic location from which they originated, such as the Soga (蘇我), the Kazuraki (葛城), the Heguri (平群), the Kose (巨勢), the Kasuga (春日) and the Izumo (出雲). By tradition those who held the kabane of omi were considered branches of the imperial line (皇別氏族, kōbetsu shizoku), and they claimed that they were descendants of Emperor Kōgen, although there is no historical evidence to support this.
The most powerful omi added the prefix Ō (大) to omi referred to as Ōomi (大臣). Examples of Ōomi mentioned in the Nihon Shoki included Kazuraki no Tsubura (葛城円) during the reign of Emperor Richū, Heguri no Matori (平群馬鳥) during the reign of Emperors Yūryaku and Seinei, Kose no Ohito (許勢男人) during the reign of Emperor Keitai and the four generations of Sogas who dominated the title during the 6th and 7th centuries: Soga no Iname, Soga no Umako, Soga no Emishi and Soga no Iruka.
When the kabane system was reformed into the eight kabane system in 684, the powerful omi of the time were given the kabane of ason, which ranked second under the new system, and omi itself was dropped to sixth in rank.
De Facto Rulers of Japan
* Figurehead refers to nominal marginalized head of state that does not hold any real power.
* Ōkimi was the ancient name for the Great Chieftain of Yamato confederacy, there was considerable power sharing with regional chieftains, Ōkimi were posthumously named Emperors (Tennō) in later eras, despite fuzzy (pre)history, the periods indicated Ōkimi are assumed to be de-facto rulers.
* 'S' symbol on ruler_title bar, years 1192-1203, stands for Shogun (tiny text area)
*3 stands for 3 rapidly swaps of Shogunate clans of Sengoku period power struggles.
*O+S means both Ōkimi and Sesshō.
* Figurehead bar: 'No' is actually 'None known' (tiny text area)
* Sesshō means imperial regent, an imperial prince or princess.