One morning on the train, Shunpei 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 Shunpei 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.

Taeko enlists Keiko's aid to cook a surprise birthday dinner for Shunpei. Shunpei confides in 'Nana' that he quit his last job because of his ex.

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.

Shunpei catches a cold, and phones 'Nana' to come take care of him. Keiko goes, but the next morning Taeko discovers her there, and yells at her.

Nana, unhappy to be fighting with Taeko, asks Yutaka to help her make up. Keiko and Yutaka meet at a bar. Shumpei shows up, and then Taeko comes, and sees Keiko and Shumpei together. She hesitates, but eventually joins. Keiko and Taeko fight, so the boys suggest they go outside. Keiko finally gets through to Taeko. She says she is going to tell Shumpei about "Nana."

Yutaka asks Keiko to be his girlfriend. She doesn't answer, but tells Taeko who says "You'll refuse, right?" That night, Shumpei shows up at Keiko's door, bringing her potatoes his mom sent him. Shumpei asks about Yutaka. Jumpei runs an event for work at the beach. Keiko and Yutaka show up. Keiko wonders if there is something between Shumpei and his coworker Ikumi.

Keiko and Yutaka start dating. Junpei gets an offer from his old company. It looks as if Shumpei will move out, and Yutaka will move in. Shumpei calls "Nana," and tells her there is a woman he is interested in, but thinks she doesn't like him. Nana(Keiko) asks "Who?" and Shumpei says "Keiko Yoda," not realizing Nana is Keiko.

Nana intends to break things off with Yutaka, but can't bring herself to do it. He kisses her. Yutaka goes drinking with Shumpei telling him about the kiss, but confesses he is worried she likes someone else. Taeko tells Yutaka that Shumpei is the one Keiko likes. Keiko and Shumpei meet. He tells her to do right by Yutaka, but she finally gets the courage to tell Shumpei he is the one she likes!

Shumpei tells Keiko to stay with Yutaka, denying liking her. Keiko is convinced he is moving, and spends Christmas eve alone. Later, Shumpei thinks about it some more, and finally realizes that 'Nana' from the phone and Keiko are one and the same. He finds her. "I thought you moved?" "Just next door." Finally, he confesses that it was her he'd loved all along.