All aspects considered, this 4th volume is one of my favourites of the series (though it still can't quite compete with the 2nd one).
The ending especially is one aspect of this volume where you can really see Kawakami grow as an author. In the previous volumes, not only did the story end on a very abrupt note, often right after the final battle, but that final battle was also a weird mix of combat and negotiating. The second part seems to be only logical since negotiation plays a fairly big part in the story. However, this mix has to be done right in order to make sense and read good, and so far this hadn't been the case in the previous books. In this volume, Kawakami splits up the two aspects: first comes the negotiating part, after that the combat. Speaking of combat, this volume's final battle was by far my favourite of the series so far. The epilogue also is the best one of the series so far. I might sound like a broken record, but the story and world-building and the writing and almost every part of this 4th volume is just so damn good. I say almost because I didn't really like Heo and Dan, to be honest. Granted, the only side characters that I really did like were the one from the 2nd volume, but I for one found Roger and Odor to much more interesting than our two new MCs. That is something taht I feel Kawakami has to work on: likeable secondary main characters.