On 18 November 1856, Atsuko married Tokugawa Iesada and became a Midaidokoro. In 1858, both Tokugawa Iesada and Shimazu Nariakira died. The 14th "shōgun" was decided to be Iesada's cousin and adopted son, Tokugawa Iemochi. Following the demise of her husband, Atsuko took the tonsure, becoming a Buddhist nun, and took the name Tenshōin on 26 August 1858, and she was given Junior Third Rank. In 1862, as part of the Kōbu Gattai ("Union of Court and Bakufu") movement, Iemochi was married to Imperial Princess Kazu-no-Miya Chikako daughter of Emperor Ninkō, and younger sister of Emperor Kōmei. The Satsuma clan brought up the request for Tenshōin to return to Satsuma, but was rejected by Tenshōin herself. In 1866, Iemochi died. Tokugawa Yoshinobu became the next "shōgun". During the Meiji Restoration, Tenshōin and her daughter in law, Seikan'in (Kazu-no-Miya's name after tonsure) helped negotiate for the peaceful surrender of Edo Castle.