I can't speak for the accuracy of the translation but the quality's very good. Your font choices are great, the typesetting is great. The translation reads well and I think the only slightly awkward thing I could spot was on the first page:
"Urgh... as expected, he's strong... the Great Demon Lord Rubulvim."
It's kinda awkward to have his name just hanging at the end of the sentence in English like that. But I also can't think of any way to word it that sounds even vaguely natural. I'll just chalk it up to 'gotta introduce the character real fast'