I've enjoyed this series to an extent, but I felt this book was pretty underwhelming. It's devolved entire to the MC doing just about everything on his own, while his harem twiddles their thumbs. Which doesn't make for a very satisfying harem story.
In this book, the MC cleans up the last major annoyances on the shard, though it takes a lot of hard work. Upon winning that epic and drawn out battle, he's given a choice to accept things as they are or accept serious challenges. Of course, he takes the challenges, and after the first 2, it's almost all solo stuff that eats up hundreds of boring pages of the MC being unstoppable. He's OP to the point that his fights aren't all that interesting. And, upon completing all these fairly easy challenges, he gets even more OP.
Then, he's off to claim is apparent Amazon bride that is the sister of his current Amazon wife. But things have happened that force her to turn him away in the name of duty. So, we get a long slog of the MC creating power armor, dueling in the arena in comically easy battles, and eventually the winning of the Amazon sister.
I'm not a big fan of the MC being a solo act most of the time. The existing harem was pushed to the side for great swaths of this book. Bridget barely had any screen time, and even his former boss turned Oni was more of an administrator than a participant. As such, this book really didn't sit that well with me. I will probably try book 5, but if it underwhelms like this one did, I'll drop the series.