Sometimes I sketch out villains in my head and the most delicious ones are queens who broke their vows for reasons that felt reasonable to them. There's the obvious hunger for power, sure, but that quickly becomes dull if you don't layer it. For me the best heretical last boss queen believes she is fixing a broken world: maybe she saw famine, watched children die, or witnessed a throne made of cruelty. Her rule turns into a kind of dark benevolence — ruthless reforms, purity rituals, and an insistence that the ends justify an empire of pain. That conviction makes her terrifying because she isn't evil for fun; she's evil for what she sees as salvation.
Another strand I love is the personal: a queen who rebels against the gods, the aristocracy, or fate because she was betrayed, loved and lost, or simply wants to rewrite what a ruler can be. Add aesthetics — she frames conquest as art, turns cities into sculptures, or treats souls like rare flowers — and you get a villain who fascinates and repels in equal measure. I always end up sympathizing a little, even as I hope for heroic resistance; it makes her story stick with me long after I close the book or turn off 'Re:Zero' style tragedies.