The heroine has a psychological illness. Her parents died in a car accident when she was thirteen, which hit her hard. She was already bad at socializing, and afterward she became somewhat withdrawn. As a child, she often hurt herself. The hero has stayed by her side ever since her parents died.
The heroine goes to college and gets a boyfriend. The hero is keeping his distance at this point. Unexpectedly, the heroine takes a large number of sleeping pills in her apartment. The hero is technically her guardian, and when the school calls him, he discovers that she is close to death.
At that point, he gets the idea to take her back to his domain.
The hero lives beyond the mortal world. Everything there lies beyond the awareness of modern people: there are sacred mountains and cultivators. He came out to carry out a mission, and the heroine was a friend he made along the way.
The feelings between a man and a woman aren't only about passionate romance. My life is longer than yours, and my world is wider. If I could, I would watch you grow old. Even if it's only what you want, I can try to give it to you. Even if it's the love you talk about, I might not know how to love, but I can learn. Rather than let you drift through the human world, I'd rather keep you by my side. Even if you only want to remain a child and never grow up, that's fine too.
