Yoon Hae-rim (Chae Soo-bin) and Uhm Gi-seok (Jang Dong-yoon), two high school students born on the same day, are raised together as neighbours since birth. They are close and precious to each other. One day, a transfer student from Seoul, Oh Dong-kyeong (Jinyoung), appears. Will it shake up the close relationship and feelings they have for each other?