The first time Hyejoo meets Yerim is at the orphanage when she's seven, a girl too cheery for her own good. 

So it baffles her when Yerim continuously sticks by her side, constantly having one-sided conversations, always trying to hold her hand (sometimes successfully), even just sitting quietly with her. It's hard to imagine why a child like her hadn't been adopted.

It surprises Hyejoo even more when she realizes how much she depends on Yerim, especially when trouble begins to follow her every step and she finds herself facing a lot more than she can handle.