Man this kid really gets it done. It's good to see a protagonist actually kill his enemy, cause I hate watching some shithead with an over 9000 power-level waffling around in a fight because he doesn't want to reveal how strong he is or doesn't want anyone to get hurt or some fucked up irrelevant stuff. Especially because Matthias is so damn efficient, he recognizes that this is inter-species conflict that can only end in genocide, because he saw it a couple thousand years ago, and he's setting about to win. It is a war, after all. It deserves to be portrayed as such.
That said, this story is flat, I mean like cardboard flat. We know maybe 5 characters, and we barely even know that much about them. The kingdom's culture, political structure, population, and just about everything are relative unknowns or hyper-simplistic. I'm not saying I want a dissertation or some shit, I just think we should see this stuff in the background to remind us that the city exists, is unique somehow and "real" people live there. The supporting cast is just there for the same gag of "wow you did the impossible, omg" and they don't even do it as well as Kenja no Mago (which is not that high a bar anyway) because we barely know them as people.