According to "Moromori-ki" (Diary of Moromori NAKAHARA), Masakado's younger brother named 'Masatane' plotted a rebellion together with TOMO no Arihari who was Masatane's father-in-law and Gon no suke (provisional vice governor) of Mutsu Province on April 12, 940.
『師守記』に天慶3年4月12日将門の弟の「将種」なる者が舅の陸奥権介伴有梁と共に謀反を企てたとある。