According to a well-known legend, Masakado and Sumitomo conspired to rebel at around the same time in order to take over the capital of Kyoto, then Masakado, a descendant of Emperor Kanmu, would become the Emperor, and Sumitomo, a member of FUJIWARA family, would become the Kanpaku (Chief Adviser to the Emperor).
二人は共に乱を起こして都を奪い、将門は桓武天皇の子孫だから天皇になり、純友は藤原氏だから関白になろうと約束したとする伝説が世に知られている。