Villain x Villain Romance

the FL is a "professional villainess" in the world of comic books but she is accidentally cast as this story's bubbly, naive, and unrealistically moral FL, while the ML is the male antagonist who was never meant to have his own love interest 

the FL is a scheming empress intent on violent revenge while the prince ML serves up his own ruthlessness with poison, treason, and wildly inappropriate lust

the main leads take turns acting as the leaders of the demon sect

the FL is a sadistic, manipulative, and cold-blooded princess who raises the slave ML to take her place as the emperor's strategist; he proves adept at filling her shoes

the prince ML and his consort FL set up the rape of a woman sent to spy on them

the FL is the Queen of Demons while the ML is her disciple, with a hidden demonic identity of his own

the FL is a trained assassin and the ML is her servant with ulterior motives; they leave a trail of bodies in their wake and not all of their victims are deserving of death