After his father Masakado, the 'new emperor,' was defeated in the Johei and Tengyo War, young Masakuni identified himself as the second new emperor with his family's support and tried to revive the government.
父の「新皇」将門が、世に言う承平天慶の乱によって滅ぼされると、まだ幼少であった将国は、一族に担がれ二代新皇を称し再興を図った。