You changed the background music using TEKKEN TUNES.

Select Tekken Tunes from the main menu and you will be greeted by pictures of stages and other things. Press A on whatever you want and just scroll down to whatever you want to change that piece of music to as long as it is not the default. Press A again to change the music and then back out of Tekken Tunes. The achievement will pop once you are on the main menu. Change the music back to default if you want.