"Cooperation Part 1" means that Jang Hye Jin and Yesung will cooperate with each other to work together. The title song "I am Behind you" is a song that has fantastic harmony and expresses in sad lyrics the heart of a person who has a crush on someone. The song has easy melody that the public can easily identify with and has harmonization in the chorus which improves the song. (Credit:sujuism.blogspot.com)
Video credit to YesungCenter
