The family name of the Taira clan was derived from "TAIRA no Ason," which was one of the official titles given to a member of the Imperial Family if they became vassals.
平氏（へいし、たいらうじ）は、皇族が臣下に下る際に賜るカバネの一つ、「平朝臣」を姓とする臣籍降下。