Okumura Rin and Yukio were brothers. Not just brothers, they were twins. And while everyone knew this objectively, Yukio was the only one who had bothered to take one simple fact into account. Being brothers meant that if Rin was the son of Satan, then powers or no, human or demon; Yukio was Satan's son as well.
Yukio was very aware of this fact. Because while Rin may have gotten the powers of Hell from their father, Yukio was sure that he had inherited his wicked, sinful heart.
He had doubted. He had succumbed to his anger and his grief over their father's death, and he had felt fear. He had not just been afraid FOR his brother, his twin, the person most important to him in this world; but he had also been afraid of him. He had feared that with the awakening of his demonic powers, Rin would not be the same, and he had pointed his gun at his own beloved brother. And when Rin had drawn his sword, Yukio had been truly terrified. He had thought that Rin was going to attack him, and he had been afraid. Afraid of Rin, afraid of the demon he had become, and when Rin had swept past him to cleave through that goblin, Yukio realized what a fool he had been for doubting him. Rin would always be Rin, and stupid and confrontational as he may be, Rin was the kindest, most loving person Yukio had ever known, and not even Satan could change that.
Yukio would allways be ashamed of this.
Unfortunately, this was not the only thing he was ashamed of. It wasn't even the thing he was most ashamed of, not by far.
Yukio loved Rin.
But Yukio did not just love his brother. He desired him.
Longed for him.
Yukio lusted for Rin.
This terrible, incestuous love he felt, that he could not suppress and could not deny; this was why he knew he really was his father's son.
It hurt. Everything about it was painful. The wickedness of his desire, the jealousy, the possessiveness. The hopelessness. The despair. The voice in his head, constantly whispering, "But it's love, isn't it? How could LOVE be wrong? Do you think it would be better if you hated him? Do you think your even capable of hating him? And aren't you supposed to love your brother? The fact that these feelings aren't what brothers normally feel to one another- doesn't that just mean your love is stronger? How could loving someone you're supposed to love be wrong? Just because it's different from normal? Aren't you two already different from normal to begin with...?"
And somehow, the thing that hurt the most was the fact that Rin loved him, too. Just not in the same way. Rin loved Yukio, respected him, had fought to protect him. But Rin could never feel the same way Yukio did; could never desire his own twin. Because unlike Yukio, Rin did not have a heart full of sin.
Yukio could not count the number of hours he had spent, just staring at his brother's sleeping form from across their shared room. Staring at the sliver of skin that would appear when Rin's nightshirt rode up amisdt his tossing and turning, at his peaceful face, at his pink lips, at the smooth muscles of his neck, at the clavicle and collarbone that beautiful throat curved into. Thinking how easy it would be to reach out and touch him. Thinking that if he just called to his brother softly and told him he couldn't sleep, Rin would wake up enough to roll to the side and move the covers over so Yukio could crawl into bed with him, they same way he did when they were children. And then, even though Rin would probably tease him in the morning, he could be beside him, feel the heat of his body next to Yukio's own, drown himself in the warmth and smell and comfort of his brother. He could even put his arms around him, or maybe just bury his face in Rin's chest, and his brother wouldn't say anything, wouldn't think anything was strange other than that Yukio must have had a terrible nightmare.
But he never did. Yukio may have a wicked and sinful heart, but it was still a heart full of love, and he would restrain his desires. He would never let his feelings be known, and never let them burden Rin. He would stand back and watch as Rin, his Rin, flirted and fawned over Shiemi, and intends to continue standing by and watching even when Shiemi or some other girl realizes just how wonderful his brother is and falls in love with him as well, because eventually someone will. And even though just the thought makes Yukio itch and burn with jealous bitterness, he will stand by and support and protect his precious brother as he inevitably builds normal relationships with real friends and gets a normal lover like he deserves, and Yukio will never breathe a word of this sinful love to anyone.
Yukio would be strong, and resist all of his wicked temptations, never giving into any of his desires towards his beloved brother, even the almost innocent ones. Because the second he gives in is the second he truly becomes his father's son, and that second is all a demon needs to slither in.
And even though it was painful, Yukio would never do anything that could harm his brother. So no matter how much love he has or how difficult it becomes to stand by and watch, that very love, the dark love burning away at him, was the same love that stopped him from acting on his sinful desires. The love that both protected and endangered Rin, the love that proved that no matter how well Fujimoto raised them Yukio was still the son of Satan, just the same as Rin.
Yukio loved Rin, in every way conceivable. And that was exactly why he needed to stay away from him.
Because no matter how right it may have felt in his heart, Yukio knew that his was a wicked, sinful love.