A Perfect Ending Plan of the Villain in a Fairy Tale

The protnist of a fairy tale whose tears turn into diamonds.
I was possessing… her bad sister.
Three years left until the passing prince fell in love with my younger sister and married, and the family who harassed the protnist were executed.
‘I’d rather go find the prince and throw in the protnist and plan a way to live.’
It was nice to find the prince after the twists and turns…
“Please marry me.”
The prince knelt on one knee. In front of me.
Not there? Don’t you have to marry my sister?
Name
Fairy Tale Villains Perfect Ending Plan, 동화 속 악역의 완벽한 엔딩 플랜