Mystic Story's rookie girl group Billie's Siyoon and Sua showed their outstanding rapping skills in their live cover of HAON's "Boom-Boom".

On October 22, a live clip of Billie's Siyoon and Sua was unveiled on their official YouTube channel. The two members performed a cover of rapper HAON's track "Boom-Boom" in stylish fashion looks and powerful charisma. Sua showed her charmingly low vocal tone and sharp rapping techniques. Siyoon continued to rap with accurate pronunciation, drawing surprise from many. In particular, Sua first drew attention as the sister of ASTRO's Moonbin and as a previous contestant on Mnet's 'Unpretty Rapstar 2'. In the performance clip, Moon Sua surprised many by showing an upgrade in skill and performance.

Meanwhile, Billie will be making their official debut in November.