She is on the surface, but I envisioned her character having a more innocent, naive, and shy side. She's been around for centuries upon centuries, since when she dies, she is reborn again in a different body. However, she's never really interacted much with anyone before due to her status as one of the four horsemen of the apocalypse.
Therefore, when she is forced to do so to protect her other sisters (being the other 3 horsemen) from being killed by a boy who plans to murder them all, and has to instead enter a marriage contract with him for 5 years, she starts to show a side of her that is far more inexperienced. While she and the boy originally hold disdain for one another, over the course of the story, they inevitably begin to get closer as they confront different parts about themselves they never truly understood.
I don't know, I only thought of this idea a few days ago, but I've been entertaining the idea in my head for some time.