Emperor Godaigo planned an anti-Shogunate movement to attack the Kamakura shogunate government, but the plan was disclosed and Emperor Godaigo was caught and subsequently exiled to Oki no shima Island in 1331 in the Genko War; when he escaped from the island in 1333, Nagatoshi welcomed Emperor Godaigo to Mt. Senjo (Kotoura-cho, Tohaku District, Tottori Prefecture) and joined the anti-Shogunate movement.
1331年（元弘元年）の元弘の変で鎌倉幕府の討幕計画が露見し捕縛されて隠岐島に流罪となっていた後醍醐天皇が、1333年（元弘3年/正慶2年）に島を脱出すると、これを船上山（鳥取県東伯郡琴浦町）に迎え、討幕運動に加わる。