K.K. Mariachi
From Nookipedia, the Animal Crossing wiki
Señor K.K.is a K.K. Slider song. It has a happy, lively, Mexican theme and uses many acoustic instruments such as the tambourine, clam shells, acoustic guitar, french horn, and trumpet. Mariachi bands are popular in Mexico and since the song is Mexican, they are an inspiration to the song. In English, "Señor K.K." means "Mr. K.K.", which is also a song available in the Animal Crossing series.
Cesar and Gala feature on the album art with K.K. Slider.
Tangy, Peaches, and Angus play it in their houses if they have a stereo.