Since the translator notes mentioned he's manga original content, I just want to say thank goodness for OC. As a LN reader and anime watcher too this series is a rare time that I find the LN source to be the inferior version in most regards. The anime and manga add in so many characters to flesh out the world. The anime, now followed by the manga, has expanded upon the mages tools and how opposing nations have taken their technology in different directions. Every time you see a mage flying about using devices akin to flying vehicles, brooms, horses, armored legs, or skis you can be thankful for extra content because the LNs really do not concern themselves with these kind of details. As far as the books are concerned everyone is flying around like they did in chapter 1 of the manga.