The Perfect Plan for a Fairy-Tale Ending

[There was a pitiful girl who cried tears of diamond and lived while being abused by her family. But a prince appeared and killed off the entirety of the evil family. And so, the girl lived happily ever after with the prince.]

...is the fairy tale, but I reincarnated as the evil sister, 'Marcia Blick'?!

This damned household! I have to escape from this house now, at least! But if I run away, what about my sister who will be left behind? I've made my decision! We're going to run away together!

'Larisa. Let's go find that prince who will make you happy!'

But: "Please marry me."

Prince, why are you proposing to me? Your partner isn't me, but my sister! This sister of yours will make you a 'perfect ending plan'!