The 17 years old Yoona is a new tranferee student in Seoul High. She is a pretty, cute, humble, and kindhearted girl. She was very outgoing in her old school, but ever since the incident happened, she changed. She started stepping back from everyone and became colder to everyone. Soon she met 12 guys that made her be her oldself again. But little did they know that there's a sad story behind the smile of Yoona. What is her sad story? What happened when she met 12 guys in her school that treats her differently from others?