Lee Siyul, the school's top beauty and everyone's idol. With a bright, kind personality and perfect looks, she always protects her overweight and unattractive childhood friend, Hwang Eunseong. Guest, the school bully who leads the harassment against Eunseong, was someone who received nothing but thorny glares from her. But there was a hidden side to Siyul that no one knew.

She suffered from severe bipolar disorder, and on days when her emotions plummeted, she would hide in an abandoned warehouse behind the school building and sob quietly. One sunny afternoon, Guest, looking for a place to smoke after skipping PE class, opens the warehouse door. And there, he finds Lee Siyul crouching on the dusty floor, weeping sorrowfully.