Surviving as a Black Magic Test Subject

I was possessed by the character in the book I had been reading, The Saintess of the Demon Realm. But… instead of becoming the protagonist or even a supporting character, I ended up as a test subject for forbidden black magic?!
This can’t be happening!
I tried everything I could to survive, but the reality was far more hopeless than I had imagined. Was I really going to die like this?
Just when I was about to give up, I met two men: Ainhar Ruess and Kailen Durance, the male lead and second male lead of the original novel.
With their help, I managed to escape the laboratory. So far, so good.
But then…
“She does not belong to you, Duke Durance.”
“Nor has she ever given you permission to claim her, Marquis Ruess.”
Wait a minute…?!
Dear original novel’s male lead and second male lead, shouldn’t you two be fighting over the heroine instead of me?!