The Atmosphere of the Novel Is in Crisis

I was transmigrated in a novel that was written by my older sister. But.. the atmosphere of the novel is a little strange? After my older sister got in a car crash, I was granted an opportunity to fulfill one wish in honor of her good deeds. So I chose to become the character my older sister cherished the most in a novel. I ended up possessing an antagonist named "Satin," but the complications didn't stop there. The main character, Cain, who is a holy knight, keeps interfering with me. "Hey, why are you looking at me like that? It's giving me the creeps." "Satin, just don't talk to me. You might as well just go die." Even though I was not really a big fan of novels. I still tried to dig into the uncovered mysterious secrets of the novel, and play as the faithful villain But... my relationship with Cain started to become deeper than anyone else's, and now everything's spiraling out of control! "Satin! I really thought you were dead... So, I was planning to kill everyone..." Kill? Seriously? Who would have thought that as a child, he was actually like a little kitten—who was feisty and stubborn?! This is really giving me a headache... (Source: Ridi, translated)