I found this very interesting comment on Reddit, and it really hit hard especially the last sentence:
"It's a painful admission as well as rejection. I think up until she was revealed to be the Haoling Princess, XL dared to hope that he had found a partner -- in fact, the casting call sheet for his character said “He had no expectations for the future until he encountered her, who had a childhood experience similar to his own. He gradually developed feelings for her, longing for a future together, only to wake up from the dream when he discovered her true identity"
But when XY basically admitted that she can't let herself fall for him and that he's not the type that a woman should fall for -- I think the first statement shut the door on him even considering courting her and the second statement was the final nail hammered to keep that door shut because I think he took it as "I could never fall for a demon" although I think she meant it as you're the kind of person that once I love you it will be too deeply and no going back.
I don't like talking about their relationship because for me personally it's very triggering. Not the physical stuff he did to her/ordered done to her in the beginning that a lot of people can't seem to get over, but all the heavy painful emotional stuff between them that is unspoken...and the message the writer seems to be sending that someone broken and abused and enslaved his entire existence doesn't deserve to be loved."
No one really talks about the overall moral of the story. And it seems to me that it just perpetuates this idea that the "different" ones deserve to be abused, to be vilified, and finally, to be denied a happy ending. We see this in countless novels, from Hans Christian Andersen to Victor Hugo. Same with all the traditional monster stories.
This is just one more example of this message. It doesn't matter if the "monster" does all those good things that only we the readers can witness. From the moment the story established that he is this violent creature that is feared by everyone, the writing was on the wall and it was never supposed to end well for him, despite all the growth and character development. I remember one commenter (BunnyFreak if I'm not mistaken) said that demons should be hunted and killed in every drama they appear in because humans hate them and that's the way it should always be. I had to read it twice to make sure such nonsense had really been written.
Anyway, the author claims that he's her favorite character and I don't doubt that, but she still refuses to break this cycle of continued abuse he's been subjected to his entire life. She gives him this semblance of self-determination by making clear to us that no matter how tragic people may perceive his ending to be, it's something that he chose for himself, as a sort of consolation for the readers. Well, of course, he could never choose anything other than that, because he himself doesn't think he deserves anything more than just dying gloriously on the battlefield.
I dislike this kind of message with a passion. I hate to see people thinking they are not worthy of a better life, that they shouldn't dare to wish for more, and instead just resign themselves to a certain fate, thinking that the world would be better off without them. If we were talking about real life, we can see this with people who struggle with addiction, or with a variety of mental disorders and other illnesses that usually make them the outcasts of society. There's nothing selfless in thinking you don't deserve more.