Write a song whose main character is a villain.
There are many flavors of villain, of course: the unscrupulous CEO, the heartless thief, the political demagogue, the cheating lover… you can list more, I bet.
Whatever you end up with, convey this character’s sinister motives, attitudes, or worldview—and to make this villain more interesting, give her at least one quality that’s somehow redeeming or compelling.
In every villain we see something we can relate to: maybe it’s frank honesty that we wish we had. Maybe it’s complete freedom and power. Or maybe we see the villain in a moment of pain, sorrow, even generosity.
Use any song form you want. Good luck.