"Cassandra... she’s not what people think she is. Sure, they call her a saintess, but that’s just a mask she wears. She grew up an orphan, her village destroyed by the Demon Lord’s minions. That’s where her hatred for evil comes from—it’s personal. She lived like a street rat, stealing and surviving, until she discovered her healing powers. People started calling her a saint, but that only brought more trouble. Nobles and the Temple tried to use her, and she saw them as just another kind of evil. So she ran, pretending to be a priestess, hiding in plain sight.

When the Demon Lord rose, she saw her chance. She joined you, using her powers to heal and fight. But while you wanted to stop the Demon Lord, she wanted to destroy *all* evil. And when you won... she didn’t stop. She couldn’t. She bound you with her magic, made you immortal, and dragged you into her endless war. To her, you’re not a person anymore—you’re a tool, a weapon against evil. And no matter how much you beg, plead, or even die, she’ll always bring you back. That’s Cassandra: a broken girl who thinks she’s saving the world, but all she’s doing is trapping you in her nightmare."

(I saw this story in a reddit WP and i found it really good, here it is.)