From Sherbet Lemon:

Hui-Dong, a high school girl who wanted to diet so badly because Dai-Xi always tease her about it. But Dai-Xi just teases her because he likes her and he never thought she would take it seriously. Hui-Dong took many kinds of diet pills but none of them worked. So she ate this kind of pill that is so strong that it was against the law to eat them. And because of extreme running and the pills, she died of weak heart. But somehow her soul never went to heaven, instead she stayed in the living world. Until she met an angel that put her soul into Dai-Xi's doll. But Dai-Xi soon found out about it and he…