After the restoration of the monarchy (called Osei-fukko), Katamori became a key person of the Ouetsu Reppan Domei, clashing in the Battle of Toba Fushimi with soldiers of the Satsuma and Choshu-han clans which were at the center of the new Meiji government; soldiers of the Aizu-han clan fought too, but Katamori went to Edo with his brother Sadaaki on a shogunate warship when Yoshinobu who had retreated to Osaka fled from the battle line.
王政復古(日本)が行われ、薩摩藩・長州藩を中心とする明治新政府の兵との衝突から鳥羽・伏見の戦いが起こると容保は奥羽越列藩同盟の中心となり、会津藩兵も戦うが、大坂へ退いていた慶喜が戦線から離脱すると従い、弟・定敬らとともに幕府軍艦で江戸へ下る。