Kosei Arima won numerous piano competitions while under the strict watch of his mother. He was known as the human metronome during that time. Since the death of his mother, Kosei Arima has been unable to hear the sound of his piano. Kosei Arima then meets Kaori Miyazono through childhood friend Tsubaki Sawabe. Kaori Miyazono plays the violin and has a free spirit. Since meeting her, Kosei Arima is able to face the piano again. Meanwhile, Kaori holds a secret.