When his older brother Nagatoshi escaped from Iki Province and raised an army while sheltering Emperor Daigo in Mt. Senjo in Hoki Province in February and March 1333, Genjo joined the army by leading monk soldiers in Daisenji Temple and others.
1333年（元弘3年）閏2月に兄長年が壱岐国を脱出した後醍醐天皇を伯耆国船上山に要して挙兵すると、大山寺の衆徒などを率いてこれに加わった。