Disclaimer: I do not own most of this. I do not own Legacy of Kain, any of the characters, or any of the dialog. I did write out observations.
Kain sat on his throne in the Sanctuary of the Clans, the seat of his once-glorious empire. Like the empire, the building itself was crumbing. He had contemptuously had it built around the ruins of the Pillars, which he had destroyed by refusing to sacrifice his own life. Centuries ago, he had made a choice to sacrifice his son for a chance to save the world.
Raziel's destiny was to become a soul-devouring entity, and then sent into the past to be trapped within the sword that Kain now held. However, Kain had found a loophole to loosen destiny's hold on his firstborn, to give him the ability to overcome his terrible fate if he chose to.
Raziel stepped through the doors, now a tattered corpse. The doors slammed shut behind him, and he turned and crouched as if they were the danger. It seemed as if he had lost much of his bravado.
Kain felt that it was time to make his presence known. "Raziel."
Raziel turned towards the throne and jumped back, ready to attack. "Kain!"
"The abyss has been unkind." Kain languidly stood. He hated to see what his actions had done to his first-born, his favorite. All that was left of his beautiful Raziel was this monstrosity. He strode towards the center of the room as Raziel approached.
"I am your creation, Kain. Now, as before, you criticize your own work," Raziel spat.
Kain accepted the fault for his actions, as necessary as they were, but he said nothing. The only way to convince Raziel that it was for the good of the world was to let him form his own conclusions.
Raziel barely took a breath before demanding, "What have you done with my clan, degenerate? You have no right..."
"What I have made, I can also destroy, child," Kain said, cutting him off. While he hadn't ordered the other clans to attack the Razielim, he did nothing to stop his other children from decimating them. Kain had abandoned the empire to its own whims that very night, and it had swiftly fallen apart without his iron control. It had been inevitable, so he decided not to fight that.
"Damn you, Kain! You are not God! This act of genocide is unconscionable!"
Kain knew that Raziel had a right to be angry, but that didn't stop him from becoming angry in return. "Conscience...? You dare speak to me of conscience? Only when you have felt the full gravity of choice should you dare to question my judgment!"
Kain knew that he should remain in control of himself, but it had never been easy. He stepped forward, forcing Raziel back. "Your life's span is a flicker compared to the mass of doubt and regret that I have borne since Mortanius first turned me from the light... To know that the fate of the world hangs dependent on the advisedness of my every deed... Can you even begin to conceive what action you would take, in my position?" He was aware that spittle had begun to fly from his lips.
Raziel reacted the way he had always had when Kain began to lose his temper. He stood strong, looked his master in the eye, and talked with a cold detachment. "I would choose integrity, Kain."
The trick still worked, and Kain was able to regain his composure. He laughed as he wondered how he could ever function again without Raziel to counter his unbalanced tendencies. Even if his child could avert his fate, it was unlikely that he would assume a role in Kain's court once again. It seemed hopeless.
"Look around you, Raziel. See what has become of our empire. Witness the end of an age. The clans, scattered to the corners of Nosgoth..." Kain trailed off. He was giving too much away. "This place has outlasted its usefulness, as have you."
Kain was aware that the fate of the world was now mostly Raziel's burden. He was also aware that he was repeating Ariel's cruelty, sending a successor on a quest that could end with his death without telling him the whole truth. Kain hoped that it would turn out different this time. He drew his sword.
Raziel held his ground for a moment, and then sensibly stepped back to put more distance between himself and his attacker. After all, everyone who had gone against the Soul Reaver in Kain's hands had died.
Kain could have struck Raziel down immediately, but he decided to draw out the battle for a time. As he established his empire, Kain had realized that he loved a challenge, and decided not to use his full abilities if he didn't have to. Kain also felt that Raziel deserved to feel his blood on his claws as a small recompense for what he had gone through.
Eventually, Kain tired of the game, having been wounded in hatred more than he liked. He would have continued it for hours, not wanting to push Raziel towards his true destiny just yet, but it would prove futile. Kain telekinetically drew Raziel towards him, forcing him to kneel as a supplicant, and brought the Soul Reaver down on his child's back.
Kain was surprised as he was blown back by the resulting explosion. Even though he had seen it in the streams of time, he had his doubts that it was the truth. He recovered his footing and looked on in satisfaction. Raziel was wounded, but technically alive. "The blade is vanquished. So it unfolds... and we are a step closer to our destinies." He laughed as he teleported away.