The Cruorlena Blood Queen and her consort The Umbrarex Lord of Shadows

The Highest servants of the Devourer are the Cruorlena (blood queen) and Umbrarex (shadow lord) The entities seek the most powerful vessel in each generation. 
The legends claim a pair of siblings seeking wealth in a cave found the Devourer and opened the Shadow Gate to his realm, they became the first queen and king and their souls have been passed down along the royal line of the Xelusians for tens of thousands of years. The truth is far more terrifying. The Cruorlena and Umbrarex are actually extra-dimensional beings who indwell the chosen vessel and demand blood sacrifices and life sacrifices to honor their parent deity. Considered the Daughter of the Devourer and the Lord of Shadows, these two entities move from generation to generation enslaving and sacrificing the people of Xelusia and harvesting their life-glow to feed their god. The Queen is considered the true ruler of Xelusia and controls her people through a form of magical seduction/manipulation called Siren's Magic. Only those with oracle, shepherding, or healer's magic can resist. The entities also taught the Xelusian people the use of blood magic and that by consuming blood and its life-glow they can access the power of the person whose blood it is. However, use of blood magic often causes insanity in those with warrior magic, and a craving for more blood like an addiction in almost everyone else. The Cruorlena also uses her magic to harvest sexual energy and suffering from her subjects. The sibling of the indwelled one is always sacrificed to seal the entities the chosen body. If the Cruorlena is bound to a weak willed host, the host will go insane with blood craving and lust and have to be put to death, or will go insane from grief and pain and kill themselves.
The Cruorlena is considered the true ruler of Xelusia. When the Dark Oracle was indwelled by the Cruorlena entity, she over came it and remained in control of herself. She mixed the Shining magic of the oracles with the Sirens' seduction magic and for the first time many Xelusians felt what it was like to be loved unconditionally. This earned her the loyalty of the population of Xelusian during her time as the Cruorlena. The Dark Oracle's suspected murder by the first princess caused civil war that led to the great Cataclysm War.
The Umbrarex or Lord of the Shadows is the consort of the Cruorlena. Like the Cruorlena, he indwells a living vessel from generation to generation. At the end of the Second Kingdom War, the entity showed an interest in indwelling the Huntsman of Adamos but instead its host was slain and it was forced to return through the Veil of Darkness into the Devourer's dimension to recover. Centuries later, it tried again. Then after the Cataclysm War and the escape of the Remnant, the Lord of Shadows indwelled Damien of Adamos, but still tried many times to persuade Lord Yurieth to accept it voluntarily.       Excerpt from The Huntsman of Adamos
  Standing alone in the room of light, Fleur looked down at the lavender gown she always seemed to be wearing in this place beyond reality; it was gray now as it had been after Kaleth's death, and as torn and stained as she felt inside. Her scars and hair were oil black and glossy. She looked nothing like she did at home. On one wall, she watched all the memories of her life with Kaleth, knowing what she did now, everything between them became suspect. She knew that on the day she had met Adamos and Kaleth for her first time, the day they had lost Damien to the Shadows, on that day Adamos must have already known who she was in spite of the thousands of years that separated his death from her birth. He had sent Kaleth to take her home and give her the oracle stone that started her on this path. She had loved Kaleth with everything in her soul but now she questioned whether or not he had ever loved her. Adamos had said Kaleth would do his duty. The centuries Kaleth distanced himself from her seemed more sinister. She had thought his guilt over killing her and the trauma of the Blood Magic Cure was what built the walls between them, but what if he had realized that he didn't want to do his father's bidding anymore, like the way Yuri resisted. They shared a home and a child, but he showed her no more love than a roommate and he left as often as he could. Work had filled the place where her pain and loneliness lived; he had only started showing he loved her again when she had almost died of self-neglect. All those centuries together, and she had not known she was simply his duty. Remembering his memorial, and the thousands of Aetherians and Humans who had released lanterns in his honor, Fleur wanted to scream out her heartache. She was glad she wouldn't go home to the future, or she might tell the truth, and their children deserved to always believe that she and their father had loved each other. The Darkness whispered to her to avenge her betrayal, “You know it was all a lie, why do you make yourself weak with concern for those who betrayed you when you have the power to avenge your pain?” Fleur turned slowly, there was a woman standing there that Fleur had never met but knew instantly who she was. The woman's shadow hair seemed to float around from some unseen breeze, her skin was matte black like the dark dust, but her eyes burned, flickering like a fire burned inside her skull. Fleur knew better than to be afraid. “You must be the Siren Queen, come to indwell your vessel and open the Gate of the Devourer so all that is living in the universe will be consumed.” “And you are the Dark Oracle, but you are not what you seem, or you would have accepted me immediately.” The entity walked around and sat down. She seemed genuinely curious about Room of Light. “What is this place?” Fleur sighed and looked around, there was no use in trying to deceive the Siren Queen. “It is a place within the Celestial Veils where oracles come to rest and soothe their souls. Don't your sirens have such a place in the Dark Realm?” It didn't answer her question. “You loved him until his death, gave him children, devotion, and it was all based on falsehood. Now, you love this one and face the same dilemma.” The queen lifted her hand and image of Kaleth and then Yurieth appeared. “I can see why you would find them desirable. They are excellent physical specimens. Strong and beautiful to behold, a Queen could get used to such companionship.” “I have seen what you would do with them, they would resist you,” Fleur retorted calmly. “Perhaps, but with my power, they could be swayed... Well, the one that still lives could be.” Glossy burning eyes regarded Fleur. “But you already know the pleasure sharing his body brings.” “Love is more fulfilling than just sex and lust.” Fleur's mouth turned down as the Siren Queen laughed. The Queen tipped its head, smirking. “Feeding from a willing lover's soul and blood at the height of passion is its own form of fulfillment.” “What are you?” Fleur asked curiously, “You're not an Aetherian or a Xelusian, neither is the Lord of Shadows nor the Devourer.” “We... My lord and I are whatever we want to be within our host bodies. We are the embodiment of the desires of our servants. We give them their every desire and they feed us.” The Queen smiled, and its teeth looked like polished onyx. “If you want him instead of the Xelusian prince, I will tell my Shadow to claim him for you and he will love you as you love him.” Images of Fleur and Yurieth together appeared, he professed his undying love on his knees and bowed before her. It was ridiculous and contrived. Fleur waved her hand, and the image froze. “It would be a lie. That wouldn't be love, it would be coercion.” Fleur mirthlessly laughed as she said it, thinking about how Adamos had ordered Yurieth to love her and probably did the same to Kaleth. Those who served the Light were the sworn enemies of the Darkness and yet they used the same tactics. “You're very bitter, Dark Oracle, I can taste it in your soul like a pungent spice. Let me teach you how to turn your pain into real power as I did your predecessor,” The Siren Queen promised. Fleur shook her head slowly. “I am already as powerful as I need to be to stop you. I am figuring out what you are.” The Queen's polished onyx teeth flashed, “And what am I? A sorceress? A temptress? A demon? You have such small definitions of things in the many languages you know. I am much more than mere words can describe, and you could be too, my daughter.” “You offer me nothing I don't already possess.” Fleur announced. “The power you offer is an illusion for the desperate, because you and I both know that magic is only limited by the wielder possessed. That is why you want me, the power I can tap is limitless, but it won't work for you because you don't know how to love.” “If your power is so wonderful then heal your eyes. You can't, can you?” The queen walked over and put its hands over Fleur's eyes. They burned cold like when she had been submerged in the Essence of Darkness liquid. When it stepped back, Fleur could feel the freezing liquid weeping from her eyes, its hands, cupped her cheeks. “When we leave this place, you will be able to see again.” The entity promised. Moving rapidly, Fleur seized the dark entity's wrists. “See falsely... And we are not going anywhere together except to the Gate, so you can return home.” Fiery eyes narrowed into slits. “You would deny me?” Clouded white eyes that saw clearly in this place blinked against the coldness, “It's not a refusal if you offer nothing.” “But I can give you everything, teach you about power, provide planets to rule, and even bring the one you love back to you. You are alone with no one to trust or love, dual wielder, you cannot continue to siphon off the Dark Powers as your Light wanes and not expect to submit to me. Without your vaulted love, you weaken every day.” The entity hissed, its hair thrashed with its anger as though it were in a violent wind. “My light will be enough for me to do what I have set my will to do.” Fleur said as she shoved the Siren Queen backwards. Suddenly, ribbons of Light wrapped the queen, subduing it, and it screamed as Fleur had once done when wrapped in chains of Darkness. The Siren Queen panted out, “I know they both betrayed you. They both killed you, your sealed ones broke one of your people's highest laws to cause you the pain of death and revival. They never loved you, only lied to use you. They should be punished, the Huntsman should be punished, and you are too weak to punish him without me.” “I don't need to punish Yurieth. I do not have the right to demand that he love me back as I love him... He should be free to love whomever his heart chooses.” Fleur whispered painfully. “I want only for his happiness and hope to find my own someday.” “You are a foolish girl,” it snarled. Shrugging, Fleur answered, “My pain is my choice, my misery is the burden of knowing they were forced to pretend to love me. It is anguish and I will admit I want to rage. I want to destroy worlds, but I will settle for destroying yours and to delay your master from emerging before I die. Your imprisonment will be enough consolation for my sacrifice. I may be a blind oracle, but I can see my path plainly.” Fleur reached out and touched the frozen image of Yurieth, he was so beautiful to her and she loved him so much, as much as she loved Kaleth when he lived. A real tear ran down her cheek as she whispered, “I would sacrifice my soul to save the one who doesn't love me because I love him. Tell me, Dust Queen, what would you sacrifice for your Lord of Shadows? Would you forever die for the Devourer?” “Release me, child of Light!” The creature struggled and thrashed. “All in good time, I will release you beyond the Gate, I suggest you hide there unless you want to die on this side with this world.” Fleur walked to where the queen writhed, she cupped its face and kissed it lightly in the forehead. “I will even save your next host to be born of a future oracle.” “What are you going to do?” The creature hissed at her and Fleur looked down on it with solid black eyes. “I am sparing you.” Fleur announced. “Because you were spared when this planet ended, and its star was shattered.” It gasped and would have pulled back if it could. “What are you talking about?” The Siren Queen had quit struggling and was staring at Fleur. “The future, oh queen of shadows. I am an oracle, remember?” Fleur answered flippantly. The walls of the room were suddenly covered in numbers and symbols. “Here's the math and magic. If you can figure it out and escape before I take you to the Gate, I might let you stop me.” Fleur laughed, she vanished from her Room of Light as the Siren Queen Entity screamed in futile rage.