Prima Donna's lead track, "Gun", contains retro influences with a western beat,[2] featuring a brass and blues feel with an electronic guitar.

In September 2013, a Star Empire Entertainment official stated that ZE:A's label-mates Nine Muses would start promotions in the second half of the year.

[6] A three-second preview of "Gun" can be heard at the end of a mash-up of the group's past singles, released onto YouTube on September 30, 2013.

Nine Muses began promoting the single on Korea's televised music shows a few days later, performing "Gun" for the first time on the October 11, 2013 broadcast of Mnet's M!

[7] The official music video for "Gun" premiered on October 14, 2013,[8] which was filmed at a sandy, deserted location with a reed forest; featuring a gas station set.