Steep Hill
From Nookipedia, the Animal Crossing wiki
Steep Hill is one of the many songs performed by K.K. Slider, being considered as a depressing piece, due to the melancholic tone throughout the song. The aircheck version of the song (played in homes) is slightly more uptempo than the live version, due to the added bassline.
K.K. Slider might choose to play the song, if the player asks for an encore and telling him that their mood is sad (a feature only available in Animal Crossing: City Folk). Nan plays this song in her house when a stereo is obtained.