Ambition Is Evil: It's never quite clear whether one of Hekat's viler acts is truly motivated by her god speaking to her from within, or just her own ambition. For example, her using a divine curse to spiritually "neuter" Vortka, rendering him incapable of fathering future children that could challenge Zandakar's ability to wield the Power Crystal (and, coincidentally, negating his own ability to do the same) could have just been her own zeal to see her dynastic plans not thwarted... or genuinely prompted by the god in order to ensure her next child would be by Nagarak, ensuring he would be much more like a typical Mijaki.
Blood Bath: Mijak's godspeakers bathe in animal blood to commune with their god.
Bloodbath Villain Origin: Hekat kills the two slavers who bought her with a divine-like curse as they had revealed her as a runaway slave to the warlord, and if the godspeakers heard, she would be nailed to a cross, disemboweled and left to die. Ironically, no actual blood is shed, and she even choses to forgo slitting their throats to use the curse.
Evil Makeover: Zandakar's hair turns blue when he uses the hammer, Dmitrak's turns red. Hekat gives herself an evil makeover.
Fantasy Counterpart Culture: According to Miller, Mijak is supposed to be like the Hittites where Ethrea is Medieval England. Tzhung-tzhungchai is obviously China, while Arbenia and Harbisland have German traits.
The Federation: The trade alliance with Ethrea, Rhian has to go through hell to get them to help her when Mijak is coming to attack.
Flat Earth Atheist: Marlan has never encountered his God before, and doesn't believe that He exists. What makes it this trope, however, is that he continues to hold this belief in the face of the divinely-chosen Dexterity Jones, even when the guy's glowing with power, and is struck down for his trouble.
The Force: Where the magic of Emperor Han comes from, called "the wind".
Freudian Excuse: Dmitrak's personality is because his mother Hekat never liked him.
Hekat herself; her own childhood was horrifically abusive (she wasn't even named and her father demanded her mother not even bother trying to teach her to talk), and the trader that she thought had rescued her by purchasing her as a slave and proceeding to treat her with exceptional kindness was really just trying to amp up her value for when he sold her as a concubine. It's not really that surprising she becomes psychotically vicious in trying to climb as high in power as she can so she can at last be "safe".
Luke, I Am Your Father: Subverted here. We know the paternity of Zandakar and Dmitrak from the first novel, neither of them are told this until the third. And in Dmitrak's case it's just before he kills his mother and gets killed himself.
Plot Hole: Mijak's Hekat chooses her name due to mispronouncing "hellcat," which she was called as a child. Ethrean sounds like English no matter what point of view it's heard from, while Mijaki is represented as a completely different language when heard by Ethrean characters. The plot hole here is how the term "hellcat" sounds exactly the same in two uniquely-developed languages.
"Well Done, Son!" Guy: Dmitrak, as mentioned above. His mother really does not like him. She only came up with the idea of having a second child able to wield the Power Crystal because she hoped that this "spare" would attract the attention of demons and thusly be a living, disposable shield for her precious Zandakar.
His efforts to win Hekat's love are even more doomed by the fact she had to lie with a man she absolutely hated and despised, the high godspeaker Nagarak (due to having earlier gelded Vortka on a spiritual level to avoid future competition for Zandakar), in order to conceive him. That he was an agonizing breach birth, requiring an unspeakably painful caesarian that she never fully recovered from, is just icing on the cake.