Their relationship was purely about power.
It was about dominating the other person, hurting him, making the other grunt with pain as fingernails were raked down his back.
There wasn't any love, any like, not even any indifference towards the other – it was just hate, pure hate, and they only had sex to relieve the tension of having to even be near one another, because sex was the only way to gain dominance without fighting or death.
And after it was done, after the haze of lust and hate had dissipated, Shinon would wonder how bad the scratches on his shoulder were – pretty bad, actually, if the stinging pain was any indication – and run his tongue over the bite mark on his lip, the faint taste of blood in his mouth. And then he'd look over at Soren – who found the ceiling to be most interesting and steadfastly refused to even acknowledge Shinon's presence – and, occasionally, ask Soren if he imagined it was Ike who was fucking him instead of himself.
Then Soren would stiffen for a moment, his fists curled up in anger, and hiss for Shinon to get out, get the fuck out right now or he'd get his fire tome and burn him to death. And Shinon would smirk, because he touched a nerve, he got him where it hurts, and then dress slowly just to piss Soren off more before he left.
Sometimes, though, when he was walking back to his room, he'd wonder if Soren cried after he left, but then he'd brush that thought off and grumble to himself about how much archery would hurt tomorrow because of his scarred shoulders.
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Uh... concrit, please. And please no throwing rocks if you don't like it. And Shinon and Soren would have like, the best hatesex ever.