How to Change a Tragedy Novel Into a Healing One

I got reincarnated! Into the prettiest, kindest, daintiest, most perfect female lead…’s little sister. The problem is that this story is an angsty R19 story. The male lead is an insane bastard with a streak of madness and my sister is doomed to be a mental wreck due to his obsession, facing a tragic ending where she loses her mind.