Nature vs Nurture
I read the whole series in one fell swoop; I was unable to pause since the unfolding of events kept me glued to the page. So since it is difficult to remember what happened exactly in each book, instead of writing a "traditional" review for each installment I decided to take a thematic/topical approach to some of the underlying questions Lindsay Buroker touches on in this series.
Since the nature of the relationship/connection between Casmir and Rache is revealed early on in a scene reminiscent of the iconic "I am your father" moment in The Empire Strikes Back, I would like to start with the nature vs nurture debate, and I feel that Buroker comes down strongly on the side of nurture.
Casmir (the, or one of the, main protagonists) and Rache (one of the main antagonists, though his role is rather ambiguous) are genetically identical, but whereas Casmir suffers from various ailments and is physically unimposing, Rache’s genes have been "cleaned up" and he has turned his body into a supreme fighting machine.
Casmir grew up in a middle class family with his two academic adoptive parents who were always supportive of him, but also let him fight his own battles, and as a sickly and scrawny kid he learnt early on to rely on his wits and to defuse potentially violent situations with his self-depricating humor. At one point his being bullied is equated with "adversity" in his formative years and it is argued that this childhood experience is what makes him such a superior problem solver. While I wouldn’t argue that point, I would disagree with calling it "adversity". Aside from his health issues and the bullying he really had almost the best upbringing imaginable: two loving parents, a stable home and community, no economic worries and he was free to pursue whatever career path he wished.
Rache, on the other hand, was the ward of an aristocratic family, about whom we don’t learn much, except that while not cruel, they were always distant. From the beginning there is enormous pressure on him to become a knight and to excel at every subject in order to be formed into the man (myth) that his genes seem to have him pre-ordained for. Not entirely unexpectedly he rebels at one point, but that rebellion is squashed in the most horrifying manner. But Rache is not subdued, and instead embarks on a path of vengeance that seems to have his self-destruction as the ultimate outcome.
So, despite Rache’s priviledged background, his physcial advantages, his combat training and military instruction I would argue that as far as upbringing/the nurture side is concerned, Casmir actually has all (or at least most of) the advantage. When they first meet that is not readily apparent. Casmir is on the run, with practically no resources, only one friend, few allies and no clue what is really going on. The only thing he has are his skills and his affable nature. Rache, while plotting towards his ultimate goal, works as a mercenary, who is equally sought-after and feared. But when he first claps eyes on Casmir he is quick to grasp the ramifications of what it means that there is another being that is identical to him, so he lets him go.
During the series Casmir and Rache cross paths many times, and despite the fact that the advantages in each encounter seem to be on Rache’s side, Casmir somehow not only manages to come out on top in their skirmishes, but Rache finds himself helping Casmir more often than not, even if events run counter to his own plans.
On a secondary level the nature vs nurture debate is also reflected in the divergent developments of the crushers. The crushers are nearly indestructible robots, designed by Casmir, first for the military and then adapted for his own protection, because of his lack of brawn. They are called Z-6000 (and from the design idea they are reminiscent of the Terminator T-1000 model), and although they all start out the same, over the course of the series (especially the latter books) they develop very different and distinct personalities, depending on their experiences, the input they receive, the people around them and how they are treated.
And in the end even Rache is changed by his "relationship" with Casmir and by his desire to find favor in the eyes of a complicated woman.