Cha Songjoo and Han Jeongseo who have lost a father and a mother respectively spend their childhood together like real siblings. Songjoo is there for Jeongseo whenever she feels lonely and has a hard time, and Jeongseo also relies a lot on Songjoo. However, after Jeongseo's father gets married to Tae Mira, Mira and her daughter Han Yoori keep harassing Jeongseo out of jealousy. Han Taehwa, Yoori's rough and wild older brother, has a crush on Jeongseo who is pure and kind unlike him.