K.K. Waltz
From Nookipedia, the Animal Crossing wiki
"K.K. Waltz" (けけワルツ) is K.K. Slider song that is played with an accordion. It also incorporates a recorder, a flute-like instrument and simple drums. Goldie, K.K. Slider, Whitney, Wolfgang, Diana, and Zell feature on the boxart. Chrissy, Cupcake, Elmer, Eunice, Sue E., and Jay all play this song in their house.