Actually, in July, Mitsunari, together with Yoshitsugu OTANI, started moving his forces and took back Nishinomaru (the castle compound to the west of the main compound) of Osaka-jo Castle.
実際、7月に三成は大谷吉継とともに挙兵すると、家康によって占領されていた大阪城・西の丸を奪い返した。