Major Land is a colorful world of music where instruments and notes come to life. During an annual concert event, Hummy, the cat songstress of Major Land, prepares to sing the "Melody of Happiness," capable of spreading happiness to worlds beyond. However, Mephisto, the king of Minor Land, interrupts the event and rewrites the score into the "Melody of Sorrow"—a dissonant composition that would instead cause despair when performed. In order to prevent this from happening, Hummy is tasked with finding the Precure, renowned warriors with an unmatched passion for music, and recreating the Melody of Happiness.