When news of TAIRA no Masakado's rebellion in Togoku and the fact that he had named himself New Emperor was brought to Kyoto, the Imperial Court was stunned; they were also concerned that Masakado and Sumitomo had conspired together to attack the east and west countries concurrently.
ちょうど、東国で平将門が謀反を起こし新皇を称したとの報告が京にもたらされており、朝廷は驚愕し、将門と純友が東西で共謀して謀反を起こしたのではないかと恐れた。