On April 17 when troops of the Satsuma army retreated from Kumamoto Castle and Ueki one after another, KIRINO and others decided to establish a new 20-km plus line of defense from the right flank in Otsu, Nagamine, Hotakubo and Kengun to the left flank in Mifune with the headquarters in Kiyama at the center to make a stand against the government army that was coming towards the south and to annihilate the government army.
薩軍諸隊が熊本城・植木から逐次撤退してきた4月17日、桐野らは本営木山を中心に、右翼は大津・長嶺・保田窪・健軍、左翼は御船に亘る20km余りの新たな防衛線を築き、ここで南下する官軍を迎え撃ち、官軍を全滅させる作戦をとることにした。