April are the voices behind "Crazy" for the 'Backstreet Rookie' OST.

The music video features Choi Dae Hyun (played by Ji Chang Wook) and his unconventional friendship with high school student and convenience store employee Jung Saet Byul (Kim Yoo Jung). "Crazy" is about feeling crazy over someone and your feelings for them.

Watch the "Crazy" MV above!