At Kichij?ji Station, Tokyo, Taku Morisaki glimpses a familiar woman on the platform opposite. Later, as his flight to K?chi Prefecture takes off, he narrates the events that brought her into his life. The story is told in flashback.

In K?chi, two years prior, Taku receives a call from his friend, Yutaka Matsuno, asking to meet at their high school. He finds Yutaka at a window, watching an attractive female transfer student whom Yutaka was asked to show around. The boys discuss their upcoming school trip to Hawaii. At the school gates, Taku is introduced to the new girl, Rikako Muto. She thanks Yutaka for providing directions to a bookstore. Taku teases Yutaka about his infatuation.

Rikako is academically gifted and good at sports, but also arrogant. Taku believes she is unhappy about leaving Tokyo. His mother learns from gossip that a divorce brought Rikako's mother to K?chi. In a phone conversation with Yutaka, he discovers that Rikako is living away from the family house.

The school year ends, heralding the Hawaii trip. Taku, suffering from an upset stomach, is stopped in the hotel lobby by Rikako. She explains that she has lost her money and asks to borrow some. As Taku has a part-time job, he lends her ¥60,000. Promising to repay him, she warns not to tell anyone. As she departs, Taku sees a stern Yutaka and feels compelled to explain. Later, Rikako admonishes him for telling Yutaka about the money, saying that he also loaned her ¥20,000.

Back in K?chi, the third year begins with Rikako making a friend, Yumi Kohama. Rikako has not returned Taku's money and he wonders if she has forgotten. Out of the blue, a distressed Yumi calls Taku, explaining that Rikako had tricked her into coming to the airport on the pretence of a concert trip, only to discover that their real destination is Tokyo, tickets paid for with Taku's money. He races to the airport, sending Yumi home, saying that he will accompany Rikako.

Upon arrival, it appears that Rikako has not forewarned her father, interrupting his planned trip with a girlfriend. Her father thanks Taku, repays the loan and arranges a room at the Hyatt Regency. Later, Rikako explains that when her parents were fighting, she had always sided with her father, but had now discovered he was not on her side. Comforting her, Taku offers his bed and attempts to sleep in the bathtub. The next morning, Rikako seems back to her normal self and kicks Taku out so that she can change clothes to meet a friend for lunch. Taku wanders around the city. After catching up on sleep at the hotel, Taku receives a call from Rikako asking to be rescued from former boyfriend, Okada, who is not as she remembered him.

Returning home, Rikako ignores Taku, but does not hide from others that they spent a night together. Taku discovers this from Yutaka, who had earlier confronted Rikako to confess his feelings toward her, but had been rebuffed. Taku confronts Rikako in class for hurting his best friend, calling her "The worst!". She responds by slapping him and he slaps her in return.

The autumn school cultural festival arrives and Rikako, who has been avoiding Yosakoi dance rehearsals, becomes more distant from the other girls, many of whom openly dislike her. Confronting her behind the school, Rikako stands firm as one girl, believing that Rikako was flirting with her boyfriend, attempts to strike her but is held back. Taku, who has seen all, approaches Rikako and comments that he is impressed with the way she handled herself. She slaps him but runs away with regret. Yutaka confronts a somewhat stunned Taku, who tries to explain. Yutaka punches him to the ground calling him an idiot before walking away. None of the three talk to each other for the rest of the year.

In the present, Taku's plane lands and he is offered a lift home by Yutaka, who explains he punched him because he'd realized Taku had held back his feelings for his sake. At a class reunion, former student president Shimizu mentions she had met Rikako earlier. She explains that as Rikako was attending Kochi University, she had flown to Tokyo for her school break, missing the reunion. Taku realizes that Rikako was the woman he'd seen at the station. Walking home, Yumi tells Taku that she too had met Rikako, explaining she could not make it to the reunion and that she wanted to meet someone, but would not say who, just that he slept in bathtubs.

In Tokyo, Taku again sees Rikako across the platforms, but this time runs to find her. As the train pulls away, he finds Rikako and realises that he had always been in love with her.

https://en.wikipedia.org/wiki/Ocean_Waves_(film)
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