Instead of My Beloved Sister, I Married a Monster

Synopsis
I inherited many things that once belonged to my dead sister.
The dresses and jewelry she treasured, the tapestries and books that adorned her room, her maids—
even her fiancé.Then, on the day my sister—whom everyone believed to be dead—returned alive,
everything was returned to its rightful owner as if it were only natural.Everything except one thing:
my sister’s fiancé—the monstrous Grand Duke, rumored to devour human hearts while they were still beating.“Die in my place, Eve. That would be better, wouldn’t it? If you die… there’s no one who would grieve for you anyway.”After realizing that my entire life had been an elaborate sham,
a fraud designed solely to make me my sister’s substitute,
I headed for the monster’s castle with one purpose alone: to die.“I heard you look like a monster.”
“I’ve never been ugly for even a single second of my life.”I was definitely planning to die, but instead—“You shouldn’t smoke so much. You’ll ruin your health.”
“Huh? I’m immortal, so it doesn’t matter. Pretty awesome, right?”
“…Where on earth did you learn to talk like that?”…So why am I living a bizarre newlywed life
with this shameless man?