the little sister loved the older sister and wanted to marry her. When the older sister got married, she spent less with her little sister making her sad.then one day, the husband got really drunked and had s** with a random girl.the older sister found out and the husband decided to divorce her.then the little sis said the little girl that had s** with the older sis husband was actually her. yeah that's the summary of the important parts.basically, the little sis is a sis-con but the older sis is not. Not sure if i'm 100% right though;need to wait for english translation