Whilst his martial prowess was outstanding, even as a poet he looked up to Toshinari; in July 1183, when the entire Taira clan fled Kyoto, TAIRA no Tadanori (the outstanding genius Kiyomori's youngest brother) handed over the capital and visited Toshinari's estate.
武勇も優れていたが、歌人としても俊成に師事し、才能に優れていた平清盛末弟の平忠度は1183年（寿永2）7月(旧暦)の平氏一門都落ちの際、都に引き返し、俊成の邸を訪れた。