One morning on the train, Shumpei points out that Keiko's slip is showing. A coworker gives her his number. Keiko calls. The two hit it off, and make plans to meet. Keiko recognizes Shumpei from the train, and embarrassed, hides from him.
Keiko's friend Taeko rents a movie. Taeko takes it to Shunpei's apartment, hoping to become his girl. The 4 go out where Keiko ends up with Yutaka's transit pass. Keiko calls Shunpei. He recognizes her as 'Nana,' and they talk.
Keiko sees Taeko kiss Shunpei. Shunpei asks 'Nana' for a photo, but she sends him someone else's. Shunpei dumps Taeko. Shunpei invites Nana to a movie, but Keiko doesn't tell him.
Nana, unhappy to be fighting with Taeko, asks Yutaka to help her make up. The 4 meet in a bar. Keiko and Taeko fight, so the boys suggest they go. Keiko apologizes to Taeko, and says she will tell Jumpei the truth about being "Nana."
Yutaka asks Keiko to be his girlfriend, but she doesn't say yes. Shumpei shows up at Keiko's door, bringing her potatoes. Keiko goes to a promotion of Shumpei's, and wonders if there is something between him and his coworker Ikumi.
Keiko and Yutaka date. Shumpei gets a job offer. It looks as if Shumpei will move out. Shumpei calls 'Nana,' and confesses that he is falling for a woman, but thinks it's one way. Nana/Keiko asks "Who?" and Shumpei says it is Keiko.
Nana wants to break things off with Yutaka, but he kisses her. Yutaka tells Shumpei he is worried Keiko likes someone else. Shumpei tells Keiko to stay with Yutaka, but she finally tells Shumpei that he is the one she likes.
Shumpei tells Keiko he has no feelings for her. She thinks he is moving, spends the day alone. Shumpei thinks, and finally realizes Nana is Keiko. He finds her. "I thought you moved?" "Next door." He finally tells her he loves her.