Around the same time Hidetada declared his intention to make Takechiyo his successor, it becomes known that Hidetada has an illegitimate child. Gou bursts in anger for being betrayed by Hidetada again, however, she realizes that she was being close-minded after seeing the child, named Koumatsu, play innocently with Takechiyo and Kunimatsu. Gou hopes to raise all of Hidetada's children together without prejudice, which eventually leads to the establishment of "Ooku," an inner palace in the Edo Castle where the wife and concubines of the reigning Tokugawa shogun live together as a family.
秀忠（向井理）は、徳川の世継ぎを竹千代（水原光太）と定めた。そんな折り、秀忠に隠し子がいることが発覚する。二度目の浮気に怒りを禁じ得ない江（上野樹里）だったが、その隠し子・幸松（後の保科正之／小林海人）が、竹千代・国松（松島海斗）と無邪気に遊ぶ姿を見て、自らの考えの狭さに気づく。正室の子も側室の子も、皆、徳川の子として暮らし育てたい。そんな江の思いが、後に江戸城大奥を誕生させることとなる。
