His father, Toshiaki, planned to cede the family estate to Shioichimaru, the paternal half-brother of Yoshishige, and had a scheme to disinherit Yoshishige together with Chikazane, his Moriyaku (guardian).
父の義鑑は義鎮の異母弟である塩市丸に家督を譲ろうと画策して、守役の親実と共に義鎮の廃嫡を企んだ。