When four major family titles which were Minamoto clan, Taira clan, Fujiwara clan, Tachibana clan had gradually prospered from the Nara period to Heian period, most of the titles of their descendants became Asomi/Ason, and the title itself became meaningless.
奈良時代から平安時代に至って、源氏・平氏・藤原氏・橘氏の四姓が隆盛になると、その末裔の姓はほとんどが朝臣になってしまい、姓そのものの意味がなくなっていった。