K.K. Sonata
From Nookipedia, the Animal Crossing wiki
K.K. Sonata is a K.K. Slider song that appeared in Animal Crossing: City Folk as a new addition to the game, and then returned in Animal Crossing: New Leaf. It has a sad, 20th century mood, and is a classical composition that has a piano soloist throughout the whole song, without any other instruments accompanying the solitary pianist. Annalise, Beardo, Miranda (in Animal Crossing: New Leaf) and Muffy play this song if they own a stereo.