The Penguin Spirit appears again and tells Shōma and Kamba to board a train and find a girl named Ringo Oginome who may possess the Penguindrum. With Ringo attending a girl's school, Shōma and Kamba send in their penguins to follow her. The brothers end up following her to a lingerie store, where they spot her maneuvering round the outside of a building in order to take a photo of something, which she shows to the brother's teacher, Mr. Tabuki. She then follows him home and hides out under his house, where the brothers conclude that she is a stalker, and pulls out a diary which allegedly fortells destined events.

Kamba goes to see Asami only to find she has forgotten all about him. He tries getting some information out of two other girls, but they are attacked by Natsume's red balls, causing them to lose their memories. Meanwhile, Shoma reluctantly follows Ringo's orders in order to let her have her diary, having him move a lot of stuff over to Tabuki's apartment, but she ends up coming down with a fever. It is revealed that Ringo's late sister, Momoka, used to date Tabuki and Ringo felt that, in order to be accepted by her family, she would have to become Momoka by fulfilling what was written in her diary. Despite her fever, Ringo sneaks off to under Tabuki's house to spend her 'first night' with him, whilst Natsume is shown to have her own penguin, discussing 'Project M' with someone.

Kanba goes to confront Natsume about the memory-erasing balls and why she desires the diary, unaware that she only has half of it. Meanwhile, Ringo is still determined to complete Project M with or without the diary, making a love potion to give to Tabuki, which actually seems to work. As Ringo decides she can't go through with it, Yuri helps her come to the realisation that she is actually in love with Shoma. As Penguin Himari brings Shoma and Ringo into a Survival Strategy meeting, Himari tells them about the day 16 years ago when Momoka died and she was born, which turns out to be the day that Shoma and Kanba were also born.

Yuri, after breaking off an affair with one of her co-stars, feels a longing for a certain someone. Meanwhile, Shoma is ignoring Ringo, feeling she will never be able to forgive him for what his parents did, and tells her they shouldn't see each other again. As Kanba tries to raise more money to pay for Himari's medicine, he is confronted by Natsume, who questions his feelings for Himari. As Ringo becomes depressed over what happened with Shoma, she is picked up by Yuri, who takes her to a hot spring inn and drugs her. It is revealed that she had a thing for Momoka and was the one who stole half of the diary that night, as she decides to act out her sexual desires on Ringo.

Ringo is approached by a journalist asking about the Takakura siblings, but she avoids him and warns Himari about him. Later that night, Himari, who was told by the same journalist about how Kanba have been collecting money for her treatment, trails him to the shop where he supposedly meet his parents just to find the place torn down and have a shocking revelation. Shouma is informed by the journalist about Kanba's involvement with the Kiga Group and tries to stop him by force with no success. Meanwhile, Tabuki and Yuri also reach the shop and just like Himari, find the skeletons of the Takakura couple before being attacked by an unknown assailant. Shouma, who finds that Kanba ordered the journalist to be killed in a car accident, and was informed by Sanetoshi that the medicine will not prolong Himari's life for long, informs her that they can't live as a family anymore and sends her to live with his uncle. Later the Kiga group, whose true leader is actually Kanba prepares themselves to make a large scale operation, and Himari, seen standing next to him, claims that she is determined to stop him at the cost of her life.

Shouma tries to dissuade Kanba with no success while Ringo also boards the train, claiming she had learned from the present she got from Himari's friends the secret spell contained into the now lost diary. She activates the spell determined to sacrifice herself to save Himari and the others, but Shouma takes the burden to himself instead while Kanba sacrifices himself to ressurect Himari for good. The terrorist attack is stopped and both Himari and Ringo are found unconsious with no memories about the brothers or everything that happened. The same occurs for Masako whose brother Mario also fully recovers. While hanging with Ringo at her house, Himari finds a message left by Kanba and Shouma and starts crying without knowing the reason why while Shouma and Kanba, in children form, pass in front of her house accompanied by the four penguins.