She is a spirit girl transformed by mysterious power, but she falls in love with the person she shouldn't love by accident. In the end, he became a demon because of love and was wiped out...
And he is the son of the vicious Demon King of the Demon Realm. He has never felt love, and he slowly falls in love with this girl who does not understand human feelings. In the end, because of his lack of control, he ruined the love of his life...