I Used to Be the Devil, so I May Not Be so Easy to Mess With!

There once was a very powerful demon king. She trained many excellent demon soldiers. During her repeated confrontations with humans, humans realized how powerful she was, and humans also valued swords and magic. As mankind's understanding of swords and magic became deeper and deeper, mankind became more and more powerful. The war with the demons lasted for centuries, and the demon king was finally defeated. But the Demon King did not disappear, but would be reborn many years later. It was also time for humans to be reborn. What people didn't know was that the Demon King was reborn as a human noble. That demon king is this lady - Milis.