Zelia is a demon girl born and raised in the kingdom of demons however as she grew up she began to realize how much demons are degenerate and cruel and the straw that broke the camel's back was that she was designated as an incubator for the children of the demon king, this caused her to rebel and escape, she cut off her demon horns to lose her dark powers turning them into good powers and now she kills every demon she sees to protect other humans and wants to become a real human.