Becoming the Villainous Duke's Family

I reincarnated into a book. And of all things, I became a terminally ill character with the same rare disease as the female lead. In the original story, the Villain retrieves the cure for the female lead, but... The problem is, I’m destined to die before the original story even begins! Rowena decides to rehabilitate the Villain—who is currently living like a complete wreck—to bring him to his senses and advance the timeline for finding the cure. “Hello, Duke. I’m from the Townsend Orphanage. My name is Rowena Whitfield, and I’m ten years old.” “……What?” “If you take me in as family, I’ll run out to the front door to welcome you whenever you come home.” “What in the world is this—” “And, I’m being really generous with this next part.” “What is it now?” “I’ll even give you a goodnight kiss before bed.” And just like that, I decided to become the Villain’s family.