Besides promoting their new single Chu~?, it was revealed on the 13th that Krystal and Luna from rookie girl group, f(x) had participated in the OST of recently debuted KBS2TV drama, Invincible Lee Pyung Kang. This is not the first time that the two have combined, having sung You're My Destiny from their new album. Their OST ballad is titled Hard and Easy and depicts the sweet love story between Lee Pyung Kang (Nam Sang Mi) and Woo On Dal (Ji Hyun Woo). With most OST MVs being just a collage of drama footage, it's refreshing to see them take a different route, as we see Krystal and Luna recording the song in the studio. Many thanks to jenpooable and babochul for tips and KpopNET for video.