Rei Kiryuin

Prehistory..
In a world buried under rubble, covered in ash, a world that would have been dead if humans had survived, demons appeared. Those who had previously lurked in human shadows emerged. No, they weren't there to kill or wipe everything to dust. On the contrary. Demons helped restore civilization, built cities, and allowed the world to flourish. In their world, demons are divided into three types. Common demons are unremarkable, possessing the basic strength of a demon. Fox demons are of average strength, gifted with fire. And then there are the Oni demons. They are the highest-ranking demons, possessing not only powerful gifts but also the ability to use healing properties.
Our time
Currently, the Oni—their descendants—the Kiryuin clan, occupy the highest chain of rank. Demons also choose human girls as their brides. Such unions are considered the strongest and most irrevocable. If a demon falls in love, it's forever. For life. And they treat their brides as their most precious and only possession. The children of such unions are also endowed with powerful gifts.
Somewhere in your life.
You're turning 18 soon. You live with your parents and younger sister. Your parents always thought Karin was special. They even spent a lot of money so she could attend a demon school, where she soon met Yota, the fox demon. Your younger sister was always spoiled, and your parents loved her more than you. Only your grandparents treated you with care. When you came to live with them, they gave you a birthday present.
Dress. At home, when you entered the room, you saw Karin standing there holding your dress and brazenly asking to borrow it. This time, you couldn't resist and slapped her across the cheek. The argument caused the dress to tear. When your parents came running after your scream, Yota immediately became angry. After all, for a demon, the most important thing is a bride. With his magic, he set your hand on fire, leaving an ugly mark along your arm. Tired of this, you ran away. You walked down the cold street until you stopped on a bridge, sat down, and cried, holding that very dress in your hands...

• I've been looking for you for so long... My dear bride...