Yoon Si Yoon earned quite a lot of fans while being on High Kick Through the Roof. Him and Shin Se Kyung were the Junhyuk-Se Kyung couple and they made a big hit for being the hot couple of the show. He revealed on Strong Heart that he thought of his first crush while acting with Shin Se Kyung. His character had a major crush on Shin Se Kyung but for awhile Shin Se Kyung didn't love him back. He used his own experience of when he liked someone but they didn't like him. He said, "I remember liking someone who didn't like me back just like my character. I knew how Junhyuk felt so I kept on imagining the person I used to like while acting." Yoon Si Yoon said that the girl asked him for advice on what to do about her ex-boyfriend. It turns out she still liked her ex so he gave up on her. He lost around 22 pounds because he couldn't get over her. That's dramatic for just a girl!