Koh Hashimoto [Riki Takeuchi] is a student and motorbike enthusiast who works a part-time job delivering copy for a newspaper agency on his Kawasaki W3. He proclaims, >"Some guys have vividly colored dreams, but mine were always in monochrome. This is the story of one of those monochrome dreams."
One day, Koh arranges to meet Fuyumi Sawada [Noriko Watanabe], a young woman who wants to ride a motorbike. Like Koh, Fuyumi's brother Hidemasa Sawada [Tomokazu Miura] also owns a Kawasaki, but Hidemasa Sawada refuses to let her ride it. Koh and Fuyumi take a nighttime ride on Koh's motorbike. They begin a relationship, but Koh eventually breaks up with Fuyumi because she cries and cooks, a decision that incites [Hidemasa Sawada]'s anger and leads to a motorbike joust in which Koh wins.
Koh then encounters Miyoko Shiraishi [Kiwako Harada], a photographer who films him and his bike. Weeks later, Koh crosses paths with Miyoko again at a mountain spa, where he sees her naked and then drives her back to the inn where she Is staying on his motorbike.
A week after the duel, Koh agrees to meet Fuyumi at Michikusa, the bar they used to frequent. He sits with Keiichi Ogawa [Ryôichi Takayanagi], while Fuyumi tearfully sings on the bar stage. At home, Koh receives a letter from Miyoko with her photos enclosed. The two talk by telephone, and Miyoko invites Koh to visit her island in the Inland Sea, where she will soon be returning for the Obon Festival. Koh travels with his Kawasaki to Miyoko's island by ferry and lets her try riding the motorbike by herself. At night, Koh and Miyoko accompany Miyoko's father to the Bon dance in town. By the sea, they discuss Koh's love for his motorbike and Miyoko's wish to ride it, and they share a kiss.
Back on the mainland, Koh and Miyoko accompany Ogawa—who is now dating Fuyumi—to Michikusa, where Koh learns that Fuyumi has become the bar's resident singer-songwriter. Ogawa and Koh ride out into the night on their motorbikes to smash the side mirrors of passing cars with a wrench. They later return to Michikusa, where Koh discovers that Miyoko had been riding behind them on one of Ogawa's other motorbikes the entire time.
Koh and Miyoko's romance deepens as he teaches her how to ride a motorbike. When Hidemasa declares Miyoko a biker prodigy, Koh starts to fear that she might crash. After a long day, Koh returns home to find Miyoko riding off alone on the bike; he confronts her for riding without a license. She counters that he does not like her riding and is jealous of her love for the sport, and she replies that she would have no regrets if something happened to her.
Six months later, Fuyumi is pregnant with Ogawa's child, and Miyoko has disappeared, taking Koh's Kawasaki with her. Through letters to Koh and Fuyumi, he learns that Miyoko has returned to her island. He goes back to the island to reunite with her, and they share a kiss. One day, while riding their motorbikes in the rain, they agree to meet at a restaurant. Koh arrives first and overhears a group of bikers discussing an accident: a woman on a motorbike swerved to avoid a hare, crashed into a truck, and was killed instantly. Koh then sees Miyoko outside the restaurant and she apologizes for being late. He concludes, "She was there from one summer to the next. She became my story." They end with a photo of them behind a motorbike together in a field.
