SEE ALSO: Birth rates in South Korea experience their largest percentage increase in nearly 14 years

The girl group opened the showcase for their new album 'REBOOT' earlier today at Seoul Hyundai Card's Understage, expressing how they felt about their transformation into a band. 

Sunmi relayed, "It felt like hitting a brick wall every time. We would get better for a while and then we'd hit a period of stagnation. I think that's when the members had the toughest time. We all stormed out of the studio to bawl our eyes out." 

Yenny added to Sunmi's comment with, "I think every one of us ran out of the studio [out of frustration] during rehearsals. It wasn't easy being in sync with one another. If one of us is missing, the rehearsal wouldn't progress so we cheered each other on and came all the way to this point." 

The two had good feelings about "I Feel You", which was composed by none other than the 'Asian Soul' J.Y. Park. Sunmi explained, "It was a sound that you don't hear much these days. As soon as I heard it, I liked it." Yenny also expressed, "I got chills down my spine. We selected the title song first and worked on the rest of the album tracks." 

All their hard work has paid off as the Wonder Girls' refreshing comeback song "I Feel You" managed to sweep eight music charts in just two hours!