The episode starts off in Satsuma in 1835, 20 years prior to the arrival of the Black Ships led by Matthew C. Perry. People in Satsuma are excited by the arrival of the heir to the domain, Shimazu Nariakira, from Edo. Meanwhile, a long-awaited daughter is born in one of the cadet families of Shimazu clan, the Imaizumi Shimazu family. The father of the girl, Shimazu Tadatake, and the mother, Oyuki, name her “Katsu,” wishing the child’s happiness. Okatsu grew up as a tomboy, much stronger than her brothers, yet is warm-hearted and full of curiosity.

Zusho's financial reform successfully clears Satsuma clan's debt, however, many people are still badly off. Young samurai, including Saigo Kichinosuke and Okubo Shosuke, feel hatred toward Zusho. Meanwhile, Zusho invites Okatsu and Naogoro to his place, asking Okatsu a favor before he heads for Edo.

Oyura, concubine of Shimazu Narioki, the clan head, plots to make her son Tadayuki an heir to the Satsuma clan which provokes a serious confrontation within a group of samurai who stand by Nariakira, Narioki's legal wife's son. Shosuke is punished for his involvement in the family quarrel. Wishing to help Shosuke's family make ends meet, Okatsu offers food and money, however, Shosuke's mother, Fuku, refuses.

Nariakira succeeds as the head of the Satsuma clan. Although Nariakira is active in reform, Kichinosuke and other young samurai are impatient that Shosuke is not granted clemency. Meanwhile, Nariakira officially invites members of Shimazu's branch families to his place. On the day of Okatsu's visit, she asks Nariakira why he has not pardoned Shosuke.

Tadatake learns from Tadayuki that his son wants to marry Okatsu. Naogoro is upset to hear the news. Meanwhile, Naogoro meets John Manjiro who had just come back from the U.S. Inspired by Manjiro's free-minded way of thinking, Naogoro tells Tadatake that he too loves Okatsu. The next day, Tadatake is called up by Nariakira where he informs his plans of Okatsu.

Tadatake is delighted with Nariakira's offer to adopt Okatsu, but Oyuki senses something is wrong with Kikumoto who brought up Okatsu. Okatsu is unable to absorb the situation and begs Tadatake to let her talk directly to Nariakira. On the morning of her visit, Kikumoto advises Okatsu that going against one's destiny is a dishonor for women.

Okatsu is deeply shocked by Kikumoto's suicide and outraged at Tadatake's insulting attitude towards her death. Meanwhile in Edo, the Tokugawa shogunate learns that an American fleet is approaching Japan, aiming to establish a trade relationship. Nariakira realizes that he needs to adopt Okatsu soon to carry out his plan. As the day of Okatsu's departure approaches, Tadatake suddenly acts cool towards Okatsu.

Moving into Tsurumaru Castle, Okatsu is unable to fit into its restrictive customs, while those women serving under her and related to the Shimazu family mock about Okatsu's humble lineage. The American fleet led by Perry sails into Uraga. While Nariakira is building up armaments against the fleet, he asks Konoe Tadahiro, head of the Konoe family to send a tutor for Okatsu.

Okatsu is being trained to be a full-fledged princess by Ikushima, a tutor brought in from the Konoe family in Kyoto while Nariakira renames Okatsu as "Atsuko" and officially begins her life as "Atsu-hime." Meanwhile in Edo, Ieyoshi, the 12th shogun of the Tokugawa shogunate, suddenly dies and his son Iesachi, who is known to be benighted, is to succeed. Nariakira confides his secret to Ikushima why he wishes to rush the training of Atsu-hime.

Ikushima is finding it difficult to train Atsu-hime who shows no interest in the training. Nariakira finally tells Atsu-hime that she is a candidate to become the wife of Iesachi, the next shogun. On that night, Atsu-hime, who attempts to escape from the castle but is easily caught, asks Nariakira his real objective. Moved by Nariakira's ambition to rebuild the unstable shogunate through Atsu-hime's marriage, she too desires to marry Iesachi.

Atsu-hime is absorbed in princess training with Ikushima. Naogoro is shocked by Nariakira's plot but is given a chance by Nariakira to see Atsu-hime again at the Star Festival. She entrusts Naogoro with her parents and the future of Satsuma. The day of Atsu-hime's departure to Edo is just around the corner.

Before Atsu-hime's departure, heads of the families related to the Shimazu family are called up to the castle where she sees her biological parents after a long time. However, she is only allowed to say some formal greetings to them. On the day of her departure as the ship leaves Satsuma, Atsu-hime cries for the first time. She vows to Ikushima that she will never cry again longing for her hometown.

Atsu-hime arrives at Satsuma clan's castle in Edo, however, she is unable to meet Nariakira's wife Fusa and adoptive mother of Atsu-hime. In Edo castle, Nariaki, former head of the Mito-Tokugawa family, opposes to Asuhime's entry in "Ooku." Meanwhile, back in Satsuma, Nariakira picks Kichinosuke to accompany him to Edo. Although Atsu-hime finally meets Fusa, she gives her a frosty look saying Atsu-hime does not deserve to become the wife of Iesachi.

Atsu-hime is depressed by Fusa's affirmation that Atsu-hime can never be the wife of Iesachi who later becomes Iesada as the 13th shogun. A new year begins and the American fleet led by Perry again appears off the coast of Edo. Nariakira is suddenly called up to Edo but before his departure, he makes a visit to Tadatake who is ill, and makes a promise which he breaks when he encounters Atsu-hime in Edo.

Kichinosuke is put in charge of preparing the traditional bride's gear for Atsu-hime. Meanwhile, Nariakira is struck down by serious illness and rumor has it that Nriakira's illness is caused by a curse of Oyura, who is plotting to make her son the head of the clan. Atsu-hime visits Oyura for the first time to confirm the rumor herself.

Nariakira recovers from his illness. Although Atsu-hime's marriage is in the final stage, Iesada shows no interest in getting married. To persuade Nariaki and to receive his approval to Atsu-hime's marriage, Nariakira invites him to Satsuma clan's castle, however, Atsu-hime argues with Nariaki about his policy on foreigners.

The marriage of Atsu-hime and Iesada is finalized and the Satsuma clan's castle is in a celebratory mood. Meanwhile in Satsuma, Naogoro is to serve under Nariakira in Edo. Only a few months later, Nariakira orders Naogoro back to Satsuma to marry Ochika, who is from a distinguished family of Satsuma clan and a younger sister of Komatsu Kiyomichi, who died of illness, to succeed the Komatsu family. After Naogoro leaves Edo, a big earthquake hits Edo.

After returning to Satsuma, Naogoro decides to marry Ochika. In Edo, the day of Atsu-hime's wedding, which was canceled after the big earthquake, is finally rescheduled. On the eve of Atsu-hime's departure to Edo castle, Nariakira confesses to Atsu-hime his true intention for arranging her marriage; if she is unable to bear an heir to the Tokunaga family, she was to persuade Iesada to make Yoshinobu, the head of the Hitotsubashi family and Nariaki's son, the next shogun.

Atsuhime moves to Edo castle where she meets Honjuin, Iesada's mother, and Takiyama who is in control of the servants at "Ooku." However, the meeting with Atsu-hime's to-be husband, Iesada, was unscheduled. She learns that he has a concubine. One day, Atsu-hime sees a man playing hide-and-seek in the garden and hears him being addressed as "shogun.

Having seen Iesada playing in the garden, Atsu-hime begins to have doubts over his sanity. On the night of the wedding, Iesada goes to sleep, showing no interest in Atsu-hime, which raised her distrust in Iesada. Ikushima finally confesses to Atsu-hime of knowing that Iesada may be benighted, but she also says that Nariakira has doubts over the rumor. Seeing Iesada playing in the garden again, Atsu-hime decides to find out the truth herself.

Atsu-hime senses Iesada must be pretending to be benighted and asks Iesada the reason. He begins to ignore and avoid her. Atsu-hime asks him to see her but he tells her that he had no intention of having a child. The information was quickly sent to Nariakira through Ikushima. Atsu-hime invites Iesada's concubine, Oshiga, to learn more about her husband. Atsu-hime feels jealous and could not resist caring about Iesada, which proved the subconscious growing affection inside her.

Atsu-hime remains unsure whether Iesada is really benighted. The U.S. begins preparing for a trade treaty between the shogunate after signing the Treaty of Shimoda, a treaty of peace and amity. Although the shogunate is pressured to decide the next shogun to face the international pressure, Abe, the chief retainer of the shogunate who stands by Atsu-hime, suddenly passes away. Overwhelmed by the situation, Atsu-hime decides to confess to Iesada that the true intention of her marriage was to make Yoshinobu the next shogun. Iesada in return confesses his secret.

Despite Atsu-hime's persuasion to name Yoshinobu successor, Iesada disagreed saying it was nonsense to recommend someone she had never met. Atsu-hime invites Yoshinobu and Tokugawa Yoshitomi, another candidate from the Kishu-Tokugawa family, to the castle to see them face to face. While Yoshinobu disappoints her, Atsu-hime was fascinated by Yoshitomi to whom laced snack was served.

As the day to meet U.S. consul general neared, Iesada tells his worries to Atsu-hime. She comes up with an idea for Iesada to maintain his dignity at the meeting and also suggests Yoshinobu's presence. Although the meeting turns out to be successful, Honjuin, who wants to make Yoshitomi the next shogun, bursts in anger, learning Atsu-hime persuaded Iesada to have Yoshinobu at the meeting.

Iesada falls ill which gave cause for Honjuin to keep Atsu-hime away from Iesada, saying his illness was caused by Atsu-hime. Although Iesada wished to spend time with Atsu-hime, the mother ordered Oshiga to be at his side. Atsu-hime sees Honjuin to clear the misunderstanding; however, Honjuin blames her for having no intention to bearing an heir to the family.

While the dispute over shogun's successor heats up, Ii Naosuke, siding with the Kishu-Tokugawa family that pushes Yoshitomi to become shogun, visits Honjuin to ally with her. Atsu-hime, under Nariakira's order to make Yoshinobu the next shogun, is driven into a corner. Nariakira submits an official statement declaring his position on the next shogun to the Tokugawa shogunate, which stirs the shogunate including "Ooku.

Atsu-hime decides not to side with neither Yoshinobu nor Yoshitomi until she is convinced who better suits as the next shogun despite Nariakira's order to push Yoshinobu. Meanwhile, Takiyama asks Atsu-hime for her support in recommending Ii as shogun's chief adviser. Although Ikushima urges Atsuhime to turn down the request, Atsuhime doesn't give an immediate answer which widens distrust between the two.

Ii becomes shogun's chief adviser and Yoshitomi is chosen as the next shogun. Iesada orders Ii and Hotta, the chief retainer of the shogunate, to entrust Atsu-hime with Yoshitomi in emergency. Suddenly Iesada suffers a stroke which fact the shogunate tries to hide even to Atsu-hime and Honjuin. Ii signs a treaty with the U.S. without the shogunate's approval. In Satsuma, Nariakira passes away. Atsu-hime shortly learns the death of another important person in her life.

Yoshitomi, the new shogun, arrives at Edo castle and is renamed as Iemochi. Tenshoin renews her hopes to become his guardian. Ikushima informs her intention to resign to take responsibility for failing to make Yoshinobu shogun. Disturbed with Tenshoin's involvement in politics, Ii begins to clamp down dissidents and asks her to reveal whereabouts of Saigo who was maneuvering to bring Ii down.

Yoshitomi, the new shogun, arrives at Edo castle and is renamed as Iemochi. Tenshoin renews her hopes to become his guardian. Ikushima informs her intention to resign to take responsibility for failing to make Yoshinobu shogun. Disturbed with Tenshoin's involvement in politics, Ii begins to clamp down dissidents and asks her to reveal whereabouts of Saigo who was maneuvering to bring Ii down.

While the Edo group and the Kyōto group inside the Ōoku continue to antagonize to each other, little by little Kazunomiya and Iemochi became closer. Tensho-in was finally feeling relieved. Then, commanding a force of a few thousand soldiers, Hisamitsu left for Kyōto with the intention of receiving the Emperor’s approval for reforming the Tokugawa Shōgunate. Meanwhile, suspicion that Tenshō-in might be involved in the plot mounted in Edo.

The Satsuma force led by Hisamitsu entered Edo accompanying an Imperial envoy. His aim was to reform the Tokugawa Shogunate. Meanwhile, Tenshō-in was anxious if Tatewaki also came to Edo accompanying Hisamitsu. Against Hisamitsu's wish, the negotiation between the envoy and Rōjū came to a dead end. Hisamitsu became extremely impatient and ordered Ōkubo to threaten the Rōjū side by force. While Tatewaki felt awkward toward such a forceful approach taken by his comrades, Satsuma succeeded in pressing on the reform plan.

A letter from Tatewaki recounting what really took place in Namamugi Incident reached Tenshō-in. Having learned the truth, she maintained that the Shogunate, together with Satsuma, needed to apologize to Britain. Meanwhile, in Kyoto, the Chōshū group came to dominate the political scene, defeating the Satsuma group and its leaders Shimazu Hisamitsu and Iwakura Tomomi.

The news that Shōgun Iemochi arrived at Kyoto came to Ōoku and lightened her mind. Kazunomiya, on the other hand, worried about Iemochi and became more restless. Her fear became true when radicals led by a Chōshū Domain group supporting the expulsion of foreigners dominated the Imperial Court in Kyoto. Mired in the quandary, Iemochi was forced to promise to the court the enforcement of expelling foreigners.

Saigo, who had been exiled, came back. At the gathering where Saigo and his old friends reunited, Tatewaki met a geisho, Okoto. The Chōshū domain, which is bent on regaining its political leverage in the capital, suddenly attacked the Imperial Palace. This is known as the Kinmon Incident. Tatewaki, who led the Satsuma forces, joined forces with the Shōgunate, along with Yoshinobu, and defeat the enemy forces. In the meantime, in Ōoku, Takiyama advised Tenshōin to let the Shogun have a concubine who could bear his heir, for she was purely concerned with the future of the Tokugawa clan and desired to consolidate the foundations of the Shugunate’s rule. Tenshōin, however, did not want to tear up the intimate relationship between Kazunomiya and Iemochi and flatly rejected the idea.