AN: Written for the spoiler_song ficathon on LJ for the prompt dark!River/Doctor, she is his shadow and he is her light.
River finds him on the battlefield, alone and bleeding. She draws her gun away from his form. A good soldier always has their gun ready, but he isn't a threat. Not like this, not lying unconscious and unresponsive. She knows he is alive; he doesn't get the luxury of death, not yet, not by anyone's hand but her own and she hasn't dealt that particular blow yet.
She kneels down, setting the gun out of his reach, just in case.
River is methodical as she runs her hands over his skin, checking for wounds but all she finds is blood and for a moment she is confused. Then it sinks in that it's not his.
Somehow, he has killed, has let the blood coat his skin like armour, but she thinks that his armour must have failed him. Or maybe he let itself fail so he could fall and slip under the weight of it all, letting himself sleep and recover.
She grins, but it is not a kind grin. Her eyes are cold, unforgiving; he has fallen so far, and she won't let him rise again. He burns too bright already; she wants to see his glow fade. Just a little. Just for a bit, she wants to smother him in the shadows until he's calling out her name: a beg, a plea, a whisper.
Slowly, she drags a hand along his chest, up past the curve of his neck until it rests gently on his forehead. She closes her eyes, and focuses her thoughts until she can see the light of him, still burning ever so brightly. She tries to crush that light, sending thoughts of pain and suffering and every dark desire she's ever had into his mind.
He screams aloud but does not wake, not now, not yet.
Once she's sure he's had enough, she opens her eyes and watches as his own fly open, panicked and desperate. His eyes settle on her after a few moments but do not linger. Instead he glances over her shoulder, to the left, and right, and back again until she places both hands on his chest, presses down on the spot where his hearts should be.
His focus returns to her and her alone.
She finds it strange how his voice has steadied. He is calm now, she realises; she has made him so.
"Sweetie," She leans down, pressing her chest against his own, and lets her hands soak into the blood she had previously mistaken for his own. "I see you've been busy without me," Then, with a grin, she brings her red right hand up and strikes it across his lips. He recoils, attempts to push her away, but she presses into him harder and kisses him with a dark purpose. When she draws away, he is still again, quiet, "You've killed, my love, how does it feel to have blood on your hands again?"
He closes his eyes and she can feel the battle within himself as she brushes against his mind.
As soon as he feels her touch he recoils again, putting up the shields that even she cannot break and when he opens his eyes to stare at her she shivers. His eyes are so dark, darker than she has ever seen them, and with a snarl he grabs her hands and pushes his body up until he's sitting with River on his lap crushed against him.
"Is this what you wanted, River?" He takes her bloodied hand and runs his own palm against it, curls his fingers around hers and squeezes until the blood squelches, almost seeps into skin with no place left to go, "Did you want to see them die? These innocent people – because that's what they were, River. They were innocent. And I killed them. Did their deaths matter or was it just their killer that interested you?"
Her face is calm as it morphs into her all-knowing smirk, "You always interest me, Sweetie. We're the same, after all, you just hide it oh-so-well. Quite the actor you are, my dear, but I can see into your mind."
River leans down, letting her lips hover against the skin of neck; breaths brushing against his pulse. She idly wonders what it would be like to bite into the flesh, to draw a gasp from his lips. She wants to see his blood run with his victims, to know that the mark on his flesh would be of her doing. She wants to cause him pain so just so can place soft kisses against the wound. She wants- no, that's not important now.
"I know what you want," she tells him, "I know what your heart desires."
"You know nothing, River," he tells her, a grin on his face this time. It makes her uneasy. It's too soft, too easy on his lips. She does not trust that particular grin, "You're too consumed by what you want to notice anyone else's' wants."
That makes her pause and that pause is all he needs, she thinks, because his grip has softened, and she places her hands on his shoulders, lets her nails sink in deep. She wishes his jacket were not in the way so she could break the skin. Regardless, the pain does not stop him from talking; it seems to spur him on more in fact.
"But I don't even think you know what you want? Do you, River? Do you know anything about yourself yet? Or are you just waiting for time to fill in the blanks for you? To give you a purpose? To give your life meaning? Do you even know what it is from me that you want?"
Her grip tightens, but she keeps her face calm. She wants him to feel, but not to see. River hates him in this moment because River wants... she wants so much, but she fears it will never be enough for her.
The Doctor burns so bright sometimes, she afraid of letting herself linger against it, against him; afraid that just as she can spread the shadows, he can swell out wide the light. She cannot run as easily as he does so she stays to hear his words. Even if it does burn, she will stay because she believes it to be right.
"No, I suppose not. After all, you've been trained to be a weapon but now you've broken free and that's good. That's very good, River, but now all those thoughts of how to kill are all you have. Well," He laughs, something almost breathless and mirth, "That and me, of course. You'll always have me. Isn't that right, Sweetie?"
Her anger flares and she pushes him down, attacks him with her lips and she is pulling at his hair and dragging nails against his bloodstained clothes. What surprises her is that he is giving it all back, but he is gentle where she is harsh, and she wants his anger unbridled. He was always good with his anger though, having the storm raging just below the surface. She's getting better with controlling her own, but she knows it will take time to wreck the same devastation in a mere glance as he does so well.
"I hate you," she hisses as she pulls the bowtie from his neck.
He laughs, peppering her jaw line with kisses that don't reach deep, "No, you don't." He says and kisses her soft and slow, drawing her away from her hate with his love.
She wonders they will always meet in these moments of hate that never seem real. His love is light and hers is dark, and together they blend with something more or less than themselves.
Later when the act is done, she'll draw her gun towards him. She'll even pull the trigger but her mark is always on something else - something meaningless to her eyes. A rock, a tree, a person. It doesn't matter, if it's not him. River could never shoot her Doctor dead. Not now, she thinks, not yet.
"One day," she begins as her forehead rests against the crook of his neck. The gun is in her holster again and her trigger finger itches against his open palm. "One day, Sweetie, I will kill you."
River understands that she is his shadow and he is her light, but that's not all the knowledge she holds. She knows that one day the light will fade and when that day comes, when the day her Doctor refuses to rise against her challenge, only the darkness will remain. When that day comes, she is prepared to do what is necessary.
"I know, River. I know. After all, it was what you were born to do."