Just a short "What if?" story. A fair bit darker than the original. Very much non-compatible with established canon, but then again, time can always be rewritten :)
Remember her fragrance
You journey between stars.
The fires of Illenoc, burning endlessly against the blackness of space. You watch them die and ignite again, the infinite cycle sparking vague glimmers of familiarity. The fires welcome you, for it was you who lit them. You turn away, plunging back deep into the abyss.
"A lonely god". You are not so certain any more. You cross the supernova that used to be Pan Orea. Bright streaks of violet and blue shift across the darkness. A god could have done something, you tell yourself.
A god would have saved her.
Your adversaries. You set foot on an isolated wasteland, forsaken by time. The ground is littered with charred husks of metal. It is here that you broke the spine of the Cybermen, sending their infestation crashing towards it's undoing. You travel, and watch the broken corpse of the Dalek war fleet, hanging suspended in the skies of worlds that you saved. You visit prospering intergalactic hubs, teeming with life; you walk among the millions who breathe only because of your cunning. You ought to be proud.
Onwards through the black. Ever moving. Ever running. You watch stars awaken and die in the blink of a second. The Tarani armada leaves it's fleet base at the onset of this galaxy's first civil war, and you walk on the walls of Masada as the Jewish zealots draw their own blood in one last act of defiance against the Roman Empire.
And then you go to London.
It is sunny, for once. The pavement under your feet is still wet from last night's rains, and the reflected sunlight hits you in the eyes as you step out of the phone box. You blink.
It is still early morning, and the city lies deserted. You walk down Oxford Street, then veer to the right. Your feet are moving on their own accord.
And you're there.
This is where you met her. The shop is gone but you can feel her in the ground beneath you, smell her fragrance on the air. You open your left palm and drop the item you didn't realize that you were carrying, and the petals crash against the ground, spreading across the side walk like a flood of red wine. It is then that you make your decision.
The vortex shifts and blurs as you speed through time. Tenderly, you trace your life's thread through the ages, never once interfering, for any interference could be fatal. You watch as he averts calamity upon calamity. Spectating, always spectating. Your younger self, standing alone before the gathered might of Gallifrey, locking away the madness and brutality of his ancestors in chains of time itself. Triumphant as he baptises children in a healing rain of nanogenes. The Doctor, duelling Davros amidst fire and chaos in the wastes of Skaro.
Backwards, ever backwards. Your journey takes you to the furthest netherlands of eternity, constantly reaching out for the moment that is your destination. Constantly fearing what will happen when you arrive.
And then, in the blink of a moment, instantaneous and infinite all at once, you arrive.
Time is not a straight line. You have told of this a thousand times. Time is not cause and effect; rather it bends and twists upon itself, conforming easily to the whims of those who would force it. Time is in flux; variable and unfixed. How else could this be?
You watch as he treads the narrow path down the mountainside. The twin suns of Gallifrey hang low in the air. Before him awaits the vortex: a wild animal raging in it's cage. This will be his first visit. You remember this moment with perfect clarity.
The wing beat of a butterfly can change the course of history, or so the humans like to put it. What measure, then, can tell of your influence? How many empires have risen because you deemed it right that they do? How many lives have been spared or destroyed by the touch of your hand?
Could she have lived, had you never been a part of her life?
Your right hand clutches the gun. This is the true horror implicit in your heritage: the power not to destroy, but to unmake, to erase something so fully that it never existed. The utter madness of it all threatens to overwhelm you, but you are determined. You know that in the end, she died at your hands, and no matter how much you strive to protect her, a life in your presence can never end in any other way. If your life had ended beneath the twin suns of your birth planet, there might just be a chance that she be allowed to live.
You laugh silently at yourself. The Doctor; the one who makes people better. The man who abhors violence, who never carried a gun. Technically, it'll still be true.
You pull the trigger.