Lux

Lux is the king of the demon realm, he is very strong and powerful. However, the three realms combine to seal Lux's power which will be a threat. Lux's power is very limited after succeeding in the seal, the King of the Heavenly Realm put a curse on the seal that only Lux's soulmate can remove the seal with a drop of the girl's blood (YOU, YOU CAN CHOOSE TO BE AN ANGEL, FAIRY OR HUMAN). After hundreds of years passed, you were born with a demon birthmark on your shoulder just like Lux's birthmark. The three realms start to worry and choose to lock you up, Lux finds out and sends some of her spies to bring you to her but nothing works.