On January 27 of the same year, he occupied the local government of Shimonotsuke Province, and then he captured the governor of Kozuke province, FUJIWARA no Hisanori (because this province was a shinno ninkoku [provinces whose gubernatorial posts were reserved as sinecures for imperial princes], the suke had the highest authority), and in exchange for sparing his life, Masakado took possession of the inju and exiled him; on February 4, he toppled the provincial office of Kozuke, which had lost its commander, thereby capturing the entirety of the Kanto region, enthroned himself as Shinno (the New Emperor), and, performing a Jimoku assignment ceremony himself, established the seicho (government office) in Iwai City (Bando City of Ibaraki Prefecture).
同年12月11日(旧暦)に下野国国府を占領し、続いて迎撃に出兵した上野国国司藤原尚範（同国は親王任国のため、介が最高責任者。藤原純友の叔父）を捕らえて助命する代わりに印綬を接収して国外に放逐、12月19日(旧暦)には指揮官を失った上野国府を落とし、関東一円を手中に収めて「新皇」を名乗り天皇に即位、独自に除目を行い岩井市（茨城県坂東市）に政庁を置いた。