DISCLAIMER: These are not the copyright holders you are looking for.
This is my first attempt at Seven!fic. The story was first posted at my LiveJournal, bewarethespork.
You see him for the first time in a mirror in the TARDIS' wardrobe room. He is a tallish, lean, large-eared man in a worn jumper and leather jacket, but his eyes, physically different though they are, are unmistakeably yours. He stares at you with something you recognise as pain in his eyes, as though the sight of you hurts him. But before you can make anything else of this strange apparition, he is gone, and you are staring at your own form in the mirror, blue-grey eyes and wayward black curls and a cream jacket over a question-mark pullover. Shaking yourself, you try to put the encounter out of your mind, but the look in his (your?) eyes haunts you, refusing to leave, and you can't help wondering what happened to him (you) to put that look of pain and grief there.
Later on, Mel notices that something's bothering you, but when she asks what's wrong, you smile, mix your metaphors and distract her by playing the spoons on the TARDIS console.
The second time you see him, he is haunting your dreams. He does not do or say anything, but merely watches, as though he sees something in you that you cannot see in yourself. What that something is, or what it could possibly mean, you don't know.
You aren't sure you want to find out.
The next day, you find yourself in front of the mirror in the wardrobe room without knowing precisely how or why you ended up there (you suspect that the TARDIS had a hand in it, the sly old girl, but there is something more to it than that, an unknown in the equation that lurks at the edge of your awareness and understanding). You stare at your reflection, examining every detail, your smug, self-satisfied smile, the fine tracing of wrinkles around your eyes, the way your brow furrows when you think, and wonder what it is he (you, you know it's you) is looking for. Oh, there's pain in your eyes, the pain of too many people gone, too many battles lost (and too many battles won), and the older pain of knowing you never belonged at home, the wildness that drove you to leave in the first place, the hunger to find whatever it is you've always been looking for. But they are old hungers and old pains, familiar companions on this journey to everywhere and nowhere. What you saw in your (his?) eyes was altogether different, and frightening both in its unfamiliarity and what it might bode for your future.
That night, you try to console yourself that he is only one possible future, repeating to yourself everything you know about unstable timelines and multiple possibilities, mantras to keep you safe, words you can wrap around yourself, insulating your sanity inside. But you can't help but notice (you were always too damned perceptive for your own good) that they ring hollowly in your ears.
"Why are you here?" you ask him the third time, as you follow him through a dream of endless, twisting corridors that lead to everywhere and nowhere. "What do you want from me?"
He stops, and turns, and smiles, and the smile is so full of bitterness it feels like a punch in the gut. "I just wanted to know," he says in a thick Northern accent that seems so unlike you that you almost think that maybe you're wrong and he's someone else (except that he can't be, because you can see your old hurts in his eyes, behind all the new ones), "how I became this." That last is said with a bitter force that shocks you.
"What do you mean?" you ask. You don't like this; it feels like a game, and not one of your own devising. You are not used to not knowing all the rules, and a part of you is frightened.
He smiles bitterly again. "You'll figure it out," he says. "Maybe a bit too late - maybe a lot too late - but you'll get it eventually."
He turns to walk away. "It all starts with you," he says, and vanishes before you can ask what he means.
The next day, on Iceworld, you find a girl with the taint of Fenric on her and decide to take her on board the TARDIS. If you can't play the future you's game, you'll settle for one where you know all the rules.
You don't see him the fourth time as you let Davros destroy Skaro, but you can feel him there, in the shadows, watching, and you feel a sudden chill, as though this act has been the start of something bigger, a series of events accidentally set in motion, like dominoes falling. You see a flicker of doubt in Ace's eyes outside the church where they're mourning Mike, and you wish you could find the words to lay that doubt to rest, but you can't, not when you share it. "Time will tell," you say, and you have to suppress a shiver, because if there's one thing you've learned, it's that it always does.
Back in the TARDIS, you stare into the mirror and pretend you can't see the shadow in your eyes.
"Kill her," you say, making your voice as cold as possible, ignoring as best you can the voice that screams that's Ace, you're hurting Ace, you can't, you have to stop. You tell yourself you're saving her, saving the universe, freeing her from Fenric, but the anguish in her voice is tearing at you and you have no choice but to harden your heart against it. One girl or the universe. You don't have a choice.
You apologise later, but the apology cannot erase from your mind's eye the sight of Ace, your dear, precious, brave, wonderful, faithful Ace, falling to her knees, defeated. You have broken her, and it is all your fault.
You see him for the fifth time in yourself. It was his voice (your voice, your fault, and you can never run away, never turn back) that destroyed Ace's faith.
Years later (a whole lifetime later, and so many lives have burned brightly and burned out before your eyes and you are too tired for this), there is a war, and you are the only one who can stop it. You understand, now - maybe a little too late - maybe a lot too late - what he (you!) meant - it all starts with you. A lifetime ago, you became the sort of man who would hurt the one person who meant the most to you in the entire universe for the greater good, and it has come back to haunt you. Gallifrey or the universe. You don't have a choice.
As this body tears itself to shreds, you just have time to appreciate the irony.
When you see him for the sixth time, he is not a dream, or a shadow, or a phantom from the future.
He is your reflection in the mirror.