Seohyun and Kihyun become friends since they are young.When she turn 13 years old she lost her memory and forgot that she and kihyun are childhood friend.She is a new student in school and become colse to Sistar.Kihyun remeber that she and him are childhood friend and he realise that she lost her memory and shs can't remeber that she and him are childhood friend.

How kihyun gonna do it? Will he help her to bring her memory back? Or not?