Faerie Phantom

I often want to tell everyone his and her story, but I don't know where to start several times. He loved her, but he had to leave her first for each other and for the path to immortality. She loved him, so she decided not to get involved. However, things change forever, and he returned to her, despite all the changes. A series of weird and bizarre cases, heinous tragedies, and dangers one after another. Why do we have no regrets and depend on each other for life and death? Maybe it's just because they made a promise to each other thousands of years ago.