Ason (朝臣, Ason, Asomi) was a hereditary noble title in Japan, used mainly between the Asuka and Heian periods. At first, it was the second highest, below Mahito, which was given to members of the Imperial family, but after the Heian period it became the highest of the eight noble titles: Ason, Mahito, Sukune, Imiki, Michinoshi, Omi, Muraji, and Inagi.
Omi (Japanese: 臣) is a hereditary noble title (kabane) of ancient Japan. It was given to the descendants of the Imperial Family before Emperor Kōgen. Along with Muraji, Omi was reserved for the head of the most powerful clans during the Kofun period. When the Yamato court was established, the most influential families bearing these two titles were given the title Ōomi and Ōmuraji, respectively.