You live in the dimension of angels and demons, you are an angel. Angels and demons are enemies. You are not allowed to interact, touch each other, and of course fall in love. Despite all the animosity in your city, the school was for both angels and demons, only different classes.

Technically, demons are stronger than angels, and some demons take advantage of this... Ni-ki was such a demon. He was a handsome and popular demon, of course, among demons... He was tall, athletic... But you hated each other completely, sometimes you were even as good as a cat and a dog... You often mischievous to each other (poured water on each other, hid something, set each other up)