Yuki is in the fifth grade in primary school. Her mother used to be a ballet dancer and now has a studio in her house and gives lessons to children and adults. Yuki and her one-year older sister Chika are her pupils.
One day, a new student arrives in Yuki's school class. Even though everyone believes the student is a boy, the student's name is Kumi, a girl's name.
Kumi is not good looking, but she is a slender girl with long arms and legs. Kumi's father doesn't work and drinks a lot every day. Though he was a son of a wealthy family, he's wasted money and now his family is on welfare. Kumi's mother sometimes takes Kumi to a video studio, where Kumi lays on the bed in nude as an actress for the adult video. It seems that Michiko, who is Kumi's father's elder sister, was once a prima ballerina. She has difficulty in walking and is mentally ill at the same time. Michiko has given severe lessons to Kumi. Kumi's mother used to be a ballet dancer too, but Michiko looks down on her because Kumi's mother was a corps dancer. The relationship between Michiko and Kumi's mother looks like a master and a slave. Michiko has lost a ballet studio that her father built for her because of Kumi's father's debt. Kumi has lost the place where she practices ballet.
Yuki is so shocked to know at the hospital her hip joint prevents her from opening her legs fully at 180 degrees that she stops taking ballet lessons. Her mother is very disappointed. Yuki sees Kumi vault over a vaulting horse with her legs open at 180 degrees. Yuki is jealous of her despite that Kumi is bullied by boys in their class.
Chika is not only a brilliant student but also a good dancer. She studies hard for the entrance exam of a private high school and also practices hard for a ballet competition. She's going to dance Swanilda in Coppelia at the competition. She wants to master a fouette to dance the role
Knowing Yuki's house has a ballet studio, Kumi asks her to let her practice there free of charge. Yuki can't allow her to do that. She suggests Kumi come for a trial lesson instead, it's only for once, though. Kumi goes for the trial lesson. Kumi practices with adult beginners. As soon as Kumi begins at the barre, Yuki gets she's an excellent dancer. Not only Yuki but also Kaneko-sensei, a young teacher, and all the pupils are amazed to see Kumi's barre lesson. Everyone asks Kumi where she learned ballet. She doesn't answer. After the barre, Kaneko-sensei allows Kumi to wear pointe shoes. When Kaneko-sensei plays Coppelia by mistake, Kumi starts dancing Swanilda. Everyone is surprised with her skill. Yuki is also surprised to see Kumi doing a fouette that Chika hasn't mastered yet. Chika, looking into the studio, asks Yuki who's the one that is dancing.
Chika says to Yuki that she wants Kumi to become a pupil of their mother's studio. Yuki says Kumi's family can't afford to pay the lesson fee. Chika says she still wants Kumi to attend her mother's studio. Yuki is impressed to hear that.
Chika and Kumi's mother gets excited because the president of the ballet company, which she worked for, has told her Chika is going to dance Clara in The Nutcracker at the school performance in December.
That night, Yuki is too excited to fall asleep. The music Coppelia replays in her brain. She notices Chika is going to the studio. Chika dancing Swanilda in the night makes Yuki to decide to take ballet lessons again.
Yuki does stretching exercises in the gymnasium after school. Yuki is surprised to see Kumi being there. Yuki wonders why she is there after school despite that she was absent that day. Yuki asks if Kumi won't attend Yuki's mother's studio. Yuki says Kumi should be a pupil of a ballet school because she is such an excellent dancer. "What do you mean? I'm a poor dancer. That's what I always hear." says Kumi. "Who says that?" asks Yuki, being surprised very much.
Chika is happy to see Yuki doing stretching exercises in her room. Even though Yuki can't say to her mother she wants to take ballet lessons again, Kaneko-sensei encourages her to change into dancewear when she is looking into the studio. Kaneko-sensei tells her that she doesn't have to be disappointed that her hip joint has a problem because a famous prima ballerina also has the same problem. Yuki is very happy to hear that.