Kidnapped By The Crazy Duke

I became a supporting character in a captivity-abduction classic novel set against the backdrop of a world war. Unlike the protagonist’s sister, who was treated coldly and abused at home, as “Diana Claire,” I was abducted in place of the protagonist in order to get out of this hell.
“Don’t leave me, princess. All right? You can’t die.”
The Duke that abducted me was a beautiful madman, an educated madman. He would visit me from time to time and stare at me as if I were an important piece of art he had carefully stored away. His eyes were ascetic yet strangely decadent, sensual yet full of flavor. I didn’t know why this man, who seemed insane, would do this to me.
What was inside the pretty wrapping paper of gentlemanly manners, elegant and graceful appearance, was a kind of madness. The man’s madness gave off a calm, eerie, and bizarre atmosphere like a work of art with a twisted meaning.
“I want to kill everyone except you, my Diana.”
She tried to control and tame this man, possessed by a cruel demon.
Originally, the word she always heard in life was “madman”.