Vol. 4
This one is a bit of a letdown in the overall arc of this manga. Book 5 actually comes up a bit short, and I can't help but feel like this book could have used a bit more room to breathe. We start off with the final secondary character, Kohaku, encountering his backstory and it just feels rushed. I think it really could have used another issue.
Else, it was pretty good overall. Art is strong as always and the final descent into the climax has begun in earnest by the 3/4 point.
Vol. 5
A great ending, and weirdly happy all things considered. Not what I expected from this author, but I was pleased about it no less. :) Everything gets pretty well wrapped up, the world is irrevocably changed, but everyone's pretty much able to make a place in the new world. I love this series. :)