This book is pretty average for haremlit. It had a few pluses, and a few minuses, and overall it just didn't satisfy me.
The MC is a serf in a post-apocalyptic world of Earth that not only had a massive alien invasion, but the collapse of society. There were some definite Fallout type scenes, even down to the lockpicking and hacking of computer terminals. The Earth was well into the future, doing genetic manipulation and having massive mech frames used to combat the aliens. And the MC ends up finding an alien AI device that hurts the story more than it helps. Just the AI's constant whining and complaining alone was reason to not have it in the story. Throw in the MC getting contaminated with an alien mutagen and not just surviving it but getting much stronger, and this one was starting to go off the rails.
The MC has 3 lovers by the end of the book, 2 of which have agreed to share him. One is a lifelong friend that's been trying to bed the MC for years. The other is someone he just met for the first time, and immediately they start to flirt and eventually have sex. The woman not a part of the harem but a lover owns a bakery, is older, and so far feels like her purpose is throwaway sex scenes. Sadly, hers are probably the best sex scenes in the book. There is a fourth woman sniffing around, a female mech "Knight" that flirts badly, and then tries to be all friendly. That one feels weird, but sounds like a guaranteed one in the next book.
The book just doesn't flow right. At times it feels like the two authors took turns writing parts, and had different visions of where the story was going.
I will not be reading a sequel to this.