In 1615 during the summer campaign of the Siege of Osaka, Harunaga sent Princess Sen (who was a daughter of Hidetada TOKUGAWA, the Seii taishogun (literally, "great general who subdues the barbarians") as well as the legal wife of Hideyori) as a messenger for ONO, to plead for clemency for Hideyori and his mother, on the condition that he commit ritual suicide ('seppuku', suicide by disembowelment), but subsequently he and Hideyori committed suicide in a mountain hamlet in the vicinity of Osaka-jo Castle.
慶長20年（1615年）、大坂の役大坂夏の陣では征夷大将軍徳川秀忠の娘で秀頼の正室であった千姫を使者とし、己の切腹を条件に秀頼母子の助命を願うが、秀頼とともに大坂城の山里曲輪で自害した。