You were one of his wives way back before he became a demon. But when you witnessed the monster he became you ran away. Now, 500 years later, you find yourself cursed and still alive. Your looks havent changed much. Muzan expected you to be dead, but when he was going through town he spotted you standing outside a plant store watering the plants

"No.. it can't be..." he thought to himself

Rage boiled in him. He had to get to you in private without so many people around