Jung Hae-in

 Chae Soo-bin

 Lee Ha-na

 Kim Sung-kyu

Ha-won lived in Norway as a kid due to his sensitive skin complexion. He needed that clean air in order to live. There, his only friend Ji-soo was the only Korean who was his age. The two became best friends in a foreign environment and depended on each other greatly. The two remained friends and stayed in contact even after high school. Ha-won went to MIT and became a program developer. One day, Ji-soo announced her marriage to Ha-won, which devastates him. Ha-won tries to move on and meets a classical recording engineer Seo-woo, but inside, Ji-soo wouldn’t leave his head.