'Soja' was exclusively used in the Oda government, the Toyotomi government and Edo bakufu (Japanese feudal government headed by a shogun), all of which rose to the central authority from the Sengoku Daimyo.
戦国大名から中央権力に上昇した織田政権や豊臣政権、江戸幕府では、もっぱら「奏者」が用いられた。