Hibiki Houjou and Kanade Minamino were childhood friends before middle school drifted them apart. When King Mephisto of Minor Land steals the Legendary Score and twists it into a Melody of Sorrow, Major Land's queen scatters the Score's individual notes across Earth to keep the sorrow from spreading. Hibiki and Kanade are chosen to become Cure Melody and Cure Rhythm and recover the notes, guided by the cat songstress Hummy and crossed at every turn by Siren, a songstress who has left Major Land behind. Patching up their own friendship matters as much as fighting Mephisto's forces.