천국의 계단.

Song Ju and Jeong Seo who have lost a father and a mother respectively spend their childhood together like real siblings. Song Ju is there for Jeong Seo whenever she feels lonely and has a hard time, and Jeong Seo also relies a lot on Song Ju. However, after Jeong Seo's father gets married to Tae Mi Ra, Mi Ra and her daughter Yu Ri keep harassing Jeong Seo out of jealousy. Tae Hwa, Yu Ri's rough and wild older brother, has a crush on Jeong Seo who is pure and kind unlike him.