
i think kiera's reaction to erez' demon linage, seems like the most genuine reaction, like this was someone she trusted, and confided in. and the big one, was developing feelings for. and i think is good for her character growth, cause yeah she did react badly, like anyone would, especailly when religion is invovled.
cause demons are beings, that she and everyone in the kingdom was taught was a unholy evil thing that would bring about the destruction to the world, and her especailly as the chosen holy maiden or whatever, was born to, kill and purify.
and her knowing the full scope of the evil that demons are capable of, like cosette(the only other demon she knows of), was well heartbroken and scared. cause he got really close to her heart. and that would be bad, for her and the of the whole world(no pressure).
i think erez did the right thing in telling her himself, rather then her figuring it out. i think she would actually kill him then, without remorse if he didn't say anything. cause he got to say his piece before bowing out. also shows how much faith he had in her.
i don't think she could kill him, even if she had to. because feelings. so now she has to get over her preconcieved prejudices, and hopefully makeup with him.
and personally, think her havinga totally chill reaction to the news would be a little undramatic and well unreal, knowing her past with cosette. also past traumas just don't go away because life is going better, one bad event, literally shapes your thinking. and i don't think she was thinking. just reacting.
I know it's yandere, but shit, haruki is a magnet for fucking crazy shirayuki is going to have his hands full forever