After he became a Buddhist priest, he called himself Myoe. When Emperor Godaigo started his campaign to subdue the Hojo family, Sadatsune sat on the fence. Although he was commanded by the Emperor to attack Hidetoki Hojo (1313), he sided with Hidetoki and jointly defeated Taketoki Kikuchi. When Emperor Godaigo recovered Kyoto,Sadatsune became afraid of reprisal and, siding with Taketoshi Kikuchi, attacked Hidetoki.
Then Takauji Ashikaga revolted against the Emperor, was defeated and fled westward to Kyushu. Sadatsune was going to join Takauji's forces when he was attacked by Taketoshi, was defeated and killed himself.