Casting RunesongsA Blurb
I haven't read the other chapters yet, but since the blurb is supposed to entire new readers, I thought I'd leave you the perspective of someone who fits that criteria.
The blurb sounds interesting. I like the direction Para 2 and Para 3 take it, and I think you've done a good job building up some mystery.
I think you could tighten the last two paragraphs quite a bit. Ideally, your blurb should fall between 100 - 200 words. (200 is the maximum allowed for Amazon listings). Your word count is over 250, so it would be good to trim some things.
I don't think you need "by a group vastly different from any they have encountered before", since you're giving us that information in the next sentence. I think you can delete that entirely, then you only use the word "attacked" once.
Further down, how does mind control magic fall into the incident that just happened? I think you can just stop at "takes his story to the humans.", and maybe expand a little on why the king is forced to send him on a mission. Is it a test? Is something needed? etc. See three paragraphs down for a continuation of this point.
Para 3 looks good. I think you meant "that hasn't been seen in 3000 years?"
Frankly, I don't think paragraph 1 is needed at all. Like the other person mentioned above, the general idea of angels vs demons isn't new. The story seems to be about Yethzer, so why not start with him? His story is what is unique, anyway.
I think you can drop "due to the strong inherited hatred in every single member", and work in the war there. Perhaps, something like "due to that they have been at war for thousands of years". The second part of Para 1 could be worked into Para 2. If you drop the part of mind control magic, and work in its place that the demons want the small strategic edge there, I think you'll not only get your wordcount under 200, but it can also make more sense why the king is "forced" to send Yethzer on a mission.
Hope this is helpful! If I missed any marks, let me know. Like I said earlier, I wanted to give you the impression from someone who hasn't read the rest yet - since this is who the blurb is written for.