Looking For The Villainess’s Contract Husband

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One day, while suffering from a fever, I realized that I had been reincarnated as the daughter of the villainess in a novel.
Thanks to recalling the original story, I became aware of the future, but it wasn’t exactly hopeful.
My mother, the villainess, would be used by others until her death, and I was destined to die from an incurable illness.
Still, there was one good thing.
Though there was no way for me to survive, I could save my poor mother.
“Mom, you’ll live. Instead of me, live happily.”
To save my mother, I went to find the duke who was a supporting character in the original story.
“So please propose to my mother, Your Grace.”
Knowing the original story, I made a deal with him, and in return, the duke rescued my mother and me from the clutches of my cruel maternal grandfather.
After successfully completing the contract, I intended to quietly face my death in a place where no one knew me…
“Libby, I think I’m feeling a bit unwell. Could you stay by my side?”
…Wait, why is this sickly-looking young man holding on to me? But seriously, is he really sick? Something seems off.