Thatcher Morvaren is Thais’s twin brother. Two of his greatest strengths are his people skills and his acting abilities, which he cultivated by distracting the villagers of Saltcrest from his sister’s supernatural abilities: “People had called me two-faced when I’d charm the village elders by day and slip into taverns by night. Sulien had always defended me: ‘He’s not two-faced—he just knows how to navigate different worlds’” (257). His quick thinking and ability to win people over become even more crucial survival skills during his time in Voldaris, “the most dangerous world of all” (257). Thatcher gets close to Olinthar so that he can spy on the god and plot his downfall, and he enters the Aesymar’s good graces so convincingly that the secret resistance believes that he’s the greatest potential threat to their cause. Even though Olinthar offers Thatcher incredible power and privilege, his commitment to his sister and their mission never wavers.

Thatcher’s self-sacrifice shapes the novel’s exploration of love and revenge. His whole life is impacted by Thais’s supernatural abilities, but he doesn’t resent her for this: “Thatcher had lost it all when my powers erupted—his chance at a normal life vanished overnight. His future, his dreams, gone. And for what? To be chained to me. To transform himself into whatever I needed. Weapon. Shield. Confidant. All without a single complaint” (595). After his powers manifest, he uses them to protect his sister, such as when he destroys the sirens during the second Trial, and to advance their shared goal of killing Olinthar. Likewise, his selfless devotion to his sister is apparent in the resolve with which he faces the prospect of being lost in the void with Moros forever: “As long as she was safe—as long as she was far from this monster—whatever happened to me didn’t matter” (722). The tragic conclusion of Thatcher’s character arc is an extreme example of the cost of revenge: He loses everything, even his memories of his sister and his own identity. During the resolution, the authors also reveal that Thatcher is Aether, the love interest of the main character in the Esprithean Trilogy, making the character a key link between the Aesymarean Duet and the rest of the Sundered Realms Universe.

Xül is the Prince of Draknavor and the son of the Aesymar of Death and a mortal priestess. In keeping with the dark romantasy genre and the enemies-to-lovers convention, Xül is at once handsome and intimidating: “He was tall and lean, built like a weapon wrapped in divine flesh. Bronze skin stretched over sharp cheekbones and a jaw that could cut glass” (75). At the start of the novel, Xül is guarded and emotionally distant because he was “raised between worlds—too divine for mortals, too mortal for the divine” (289). Xül’s aloof demeanor is also the product of trauma. He was mercilessly bullied by his divine peers, and he coped by withdrawing into his studies and using knowledge as both armor and ammunition against those who would harm him: “When I entered the Trials, I knew every weakness, every fear, every secret shame of those who had tormented me” (302). Xül’s cleverness and expertise help Thais survive the Trials of Ascension, such as when he teaches her the alchemical skills she employs during the first Trial. Xül also possesses a deep capacity for devotion. At first, he expresses this by fulfilling his duties to his realm, but he later shifts his passion to Thais, professing that he would “burn Voldaris to the ground for [her]” (620). Xül’s hidden vulnerabilities, cleverness, and devotion facilitate his chemistry with Thais.

As the protagonist’s love interest and an occasional narrator, Xül shapes the novel’s genre and meaning. Over the course of his and Thais’s slow-burn romance, he transforms from aloof strategist to passionate lover. Just as Thais changes him, Xül advances her character development in turn. He helps her master her power and shifts her perspective on revenge by convincing her to fight not just for Olinthar’s death but also her own survival: “The Thais I know would spit in the face of inevitability. She wouldn’t accept death as a foregone conclusion” (240). Xül’s dynamic characterization is closely linked to the themes of love and destiny. He believes that he “was born a pawn in a game larger than [him]self” and spends most of the book resigned to the life—and wife—his father chooses for him (300). However, his bond with Thais leads him to place his romantic love above his once sacrosanct familial and political loyalties to the extent that he’s willing to jeopardize the resistance movement’s success to protect Thatcher. At the end of the novel, Xül demonstrates the complexity of love by remaining devoted to Thais despite the complications of his arranged marriage and his bargain with his father, intensifying the romance and tragedy of the resolution.

Olinthar is the King of Gods, who is secretly possessed by Moros, the Primordial of corruption. Ironically, the two characters’ domineering, manipulative personalities have much in common. Moros’s ambition led him to feed on his fellow Primordials’ memories, and Olinthar’s desire for “absolute control” prompted the gods to betray the Primordials and seize control over the universe. Olinthar has golden eyes and gold-streaked hair, symbolic reminders of his divinity, and usurping the Aesymar’s face and authority allows Moros to present himself as a “benevolent” leader, all while plotting to conquer all the Sundered Realms.

Moros and Olinthar’s cruelty sets the story into motion by causing the main character’s conception and placing her on the path of vengeance. Although Olinthar is the Aesymar of Light and Order, the hypocritical god abuses his power and violates divine law by sexually assaulting Thais and Thatcher’s mortal mother. Thais’s primary motivation is killing Olinthar, a goal that gives rise to the theme of the cost of revenge: “He’d created us through violence. It seemed fitting that violence would be what destroyed him” (93). Olinthar also contributes to the theme of self-determination versus destiny. Thais sees destroying him as a chance to rewrite her fate, but she fears that she’s playing into destiny’s hands by using the supernatural powers she inherits from him.

Olinthar and Moros figure prominently in the story’s most suspenseful moments, such as their climactic battle with the twins. In addition, the plot twist that the Primordial is possessing the King of Gods raises the novel’s stakes. Even though Thais achieves her goal by killing Olinthar, the victory seems hollow because an even greater threat is loose in the universe: “The implications crashed over us. […] Moros with knowledge of all our secrets, our weaknesses, our plans. And now Thatcher—with power that could rival a Primordial’s—lost in the ether where Moros could reach him” (699). Although Olinthar is the novel’s main antagonist, Moros represents an even greater threat to Thais, her allies, and the Sundered Realms as a whole. The novel’s final chapters thus position him to take over the role of primary antagonist in the sequel.

Morthus is Xül’s father and the Aesymar of Death. He’s the second most powerful deity and rules the most feared world in Voldaris. His intimidating presence reflects his vast might and forbidding role in the pantheon: “The God of Death was even more imposing up close—handsome with black hair and pale skin that seemed almost luminous in contrast to his completely black eyes. When he looked at me, it felt like being examined by the universe itself” (284). Morthus’s tenderness toward Osythe contrasts with his fearsome reputation and adds to his round characterization. The couple’s mythic love story is introduced early in the novel, providing the first indication that not all gods support the status quo and foreshadowing the revelation that Morthus leads the secret resistance against Olinthar: “Morthus proves that even gods can choose love over law, compassion over command” (45). Because he is greatly moved by mortals’ sufferings and the ways that they are treated as “pawns in immortal games” (705), he is willing to commit “necessary sins,” such as plotting Thatcher’s death, for the sake of the rebellion. At once compassionate and coldly calculating, Morthus is a complex, morally gray character.

Morthus plays multiple important roles in the story as Xül’s divine parent, the leader of the rebellion, and Olinthar’s successor. He contributes to the theme of self-determination versus destiny by pressuring his son to sacrifice his personal happiness and marry Nyvora out of duty to his family and world. Morthus is also a key figure in the authors’ exploration of the cost of revenge. He believes that the end justifies the means, and he threatens to kill Thais to protect his goal of a reformed pantheon: “[T]he end is a realm where children aren’t harvested for divine amusement […] I’ve done terrible things to get us this far. I’ll do worse if needed” (705). Morthus’s ruthlessly utilitarian commitment to his plan makes him one of the architects of the story’s tragic ending: The bargain he forces Xül to make for Thais’s life prevents the couple from being together, and the suspense and pathos escalate when Thais is left questioning whether the universe had “simply traded one tyrant for a cleverer one” at the end of the story (710). Although Morthus shares Thais’s goal of ending Olinthar’s corruption, his willingness to sacrifice the people around him to achieve that objective places him in an antagonistic role.