When the Winter Campaign of the Siege of Osaka happened, Kunimatsu entered the Osaka-jo Castle together with Jokoin in order to avoid investigation as the illegitimate child of Hideyori.
大坂の役大坂冬の陣が起こると、秀頼の隠し子との詮議を受けぬよう、常高院と共に大坂城に入城。