The Phoenix Won't Return to Its Nest: Imperial Uncle, Don't Even Think of Escaping

A modern military doctor transmigrates into the body of a frail, chronically ill deposed empress. She only wants to live quietly and take care of her health, but the powerful imperial uncle keeps forcing her into a corner. When the realm falls apart, she finally reveals her fangs. Only then does he realize that the pitiful girl he took in is no helpless waif, but a female demon capable of turning the world upside down.