Natsumi is an editor at a major publisher and her husband, Kazuhiro, works at a rival company. After 8 years of marriage, they have no children, and Natsumi still uses her maiden name.
Natsumi and Kazuhiro, post-separation, bump into each other at an author's funeral. The two have dinner, reconnecting over work, books, and many, many drinks, ending with them in bed together.
Natsumi is at work when she realizes she left her phone. At that very moment, Naruo rings her and Kazuhiro, who dropped by the house, picks up. Kazuhiro grows suspicious.
Natsumi visits Naruo at his house. Kazuhiro calls out of the blue. Natsumi doesn't pick up, but still rouses Naruo's suspicions.The next day, Natsumi tries to persuade Shohei to write his next piece for her.
Kyoko tells Natsumi she saw Kazuhiro and Fuyuko at the movies. Natsumi is curious about the girl, and wonders how she compares to Naruo. Director Fujii presses Natsumi to pursue signing Shohei, telling her to "teach Kazuhiro a lesson.
Natsumi runs into Kazuhiro at an author's end-of-year party. Unexpectedly, Kazuhiro does an about-face on his previous plans, saying he doesn't want to divorce her and wants to spend Christmas with her instead of Fuyuko.
Fuyuko calls Natsumi's office and asks her to meet up.Despite being a homewrecker, Fuyuko is bold and unapologetic towards Natsumi, plainly telling her she should leave Kazuhiro.
It's spring, and Shohei's book is published. Natsumi runs into him at a bookstore, and they grab drinks together. Things become tense when Kazuhiro and Fuyuko walk into the same restaurant.
Kazuhiro splits up with Fuyuko. Natsumi tells him that she is in love with someone else and can't live with him anymore. She moves in with Kyoko and starts visiting Naruo every day.
