A/N: So I haven't seen this sort of fic on this site before. Yay me for originality! But yes. My version of why there isn't a Rose Tyler in Pete's World.
A golden mists envelopes her, and her jaw drops and she screams his name. Gradually, the universe blows away the atoms of Rose Tyler, and she is no more. He stands there, shuddering, only barely comprehending what's happened. And then he's down on the floor, fingers entangled in the remaining dust with the burn of loss scorching his features.
0000
The process is smooth, like cold velvet. For a moment she thinks she's survived, that if she just turns around she'll see the relieved smile of her love. But then she remembers the warmth around her waste, and her hope comes crashing down all around her. Her mouth is open, her eyes wide, and every molecule of her existence denying that she's lost him. Seconds later, when she's retracted from her not-father's grasp, she aches for something that's died inside of her.
0000
It's not every early twenty-first century Tuesday you see the impossible. But there she is, expression schooled into polite indifference as she marches through the London rush. He refuses to believe she's there – she simply doesn't exist, after all. But he's been running for so long while he's so irreversibly broken, and like any machine with a kink, that Time Lord logic malfunctions, and now he's running toward her like she's the only thing keeping him alive.
0000
These days, she's always running. Torchwood drags her all around the world as she chases down alien outbreaks, always constantly struggling between being Earth's diplomat or its defender. Tuesday the fourteenth is like any other Tuesday, save for the hand on her arm on the street. Immediately, she's round on her heel and poised to beat the hell out of the pervert that thinks he can cop a feel out of Pete Tyler's daughter, but that is before she comprehends the ice-blue eyes that meet her hazel ones.
Her gaze drops down, and the lines in her brow soften as her eyes devour the sight of the jumper and leather jacket she used to be so fond of. When she looks up again, she can't help that hot tears welling in her eyes as she says, "You're not supposed to be here."
"Neither are you," the Doctor returns, his tone hard and unforgiving, stirring memories of show window dummies and that first word he said to her. Noting her slight wince – he always was a keen observer of people – he tries to school his expression into something more appealing. He fails, but Rose agrees anyway when he suggests they talk about it somewhere else.
0000
They don't speak until they reach the old chip shop she used to frequent, and the whole scenario is so painfully familiar and yet so completely different from the sun-kissed images she has of the time they had together. She slides into her old booth, and his expression is totally unreadable – another strange-yet-known experience for her. This incarnation -- so wounded and vulnerable and sarcastic and cold -- was an open book to her before the regeneration. After Christmas, he was all bananas and winks and sort of brown. Now he's blank again, not a trace of emotion carved in his features.
"Who are you?" he asks, and Rose almost smiles. She's forgotten how blunt he once was.
She catches the flash of his irises, and knows that he is wondering why she's amused. "I would tell ya," she says, "But I've got timelines to maintain. Don't want any Reapers showin' up or anythin'" She attempts to really smile at him, but is quickly discouraged. No more is he a blank of sheet of paper, but rather an illustration of pain and anger and the ever-persistent loneliness. Somehow, she doesn't even flinch, but wonders we she might've said to provoke this reaction.
"No," he murmurs, his voice painstaking even, "We wouldn't want that." The Doctor's gaze flicks up to hers, and they stare at each other for a moment, a silent battle of their equal wills before he relents.
"I met Rose Tyler in two-thousand and five. I had to ask twice before she said yes. We went to the year five billion to watch the Earth explode and then met Charles Dickens. I took her back home a year late, and her boyfriend blew up Downing Street. She met a Dalek and saw the soul in it, and then drank and beef-and-chicken flavored milkshake on Satellite Five. And then she asked me to take her to the day her father died."
The tensing of his muscles is brutally obvious, and he's sort of hunching his back, staring down into his fists. Rose recognizes the motions all too well.
"Major paradox, that. The Reapers had a very precise way of fixing it. With the TARDIS gone, I had no chance of stopping it. It only took a few tweaks of your timeline. It's the simple schemes that fool you in the end."
He looks at her, and she's burning and drowning all at once, her empathy submerged in his loss. Somehow, her voice is even when she says, "So…Pete and Jackie still existed. Just, never thought about having any children?"
The Doctor nods. Leaning in closer, "You were gone. Nothing. Rose Tyler never existed. You were – oh, Rassilion – it was like remembering a dream. Slipping away. I thought you were a dream. I thought I'd imagined you. But no," his expression shifts, into a sort of bittersweet affection, "You, Rose Tyler, are far too innocent to be imagined."
Rose exhales. The emotion between them is electrifying and dangerous and she knows if she doesn't play her cards right she'll hurt this Doctor more than her other's absence ever could.
"I'm not from this universe," she blurts, "I'm not your Rose."
He swallows, looking down. She can't see his mouth moving, but hears a strangled utter of, "I know." Looking up, "You're positively itching with void stuff." He has another one of those smiles, like he's disappointed – disappointed, she realizes, because she isn't his Rose.
Her surprise is rather embarrassing evident. "But – how? You're not wearing those 3D glasses things." She waves her hand in the general direction of his face to demonstrate. He snorts, quirking an eyebrow.
"Who told you that? That's the most primitive way to detect void stuff in the book. I can see it just by looking at you. Time Lord thing, y'know."
Rose rolls her eyes at his arrogance, but is unable to keep the smirk off her face as he has inadvertently insulted himself.
"But I still need an explanation, Rose Tyler. Traveling between the universes is impossible." He regards her coolly, challenging her.
Bitter irony is the force that persuades her to quirk the corner of her mouth into a sharp smirk. "I don't think that word means what you think it means."
His gaze is unfaltering, choosing not remark on how she has gone all The Princess Bride on him. Rose exhales, looking away as she turns her eyes skyward. She has become unfamiliar with his stubbornness. Relenting, she speaks.
"You died." She isn't sure why she starts with this, and doesn't dare to look at him. "The Reapers, they sort of…ate you. We didn't know what to do. But my dad…well, he figured it out. Said you figured it out long before. He went out to the street…right in front of that car that was s'posed to…" Rose exhales once, gathering her resolve. She looks up, her expression clean as paper. "To kill him. The paradox corrected itself, and he came back. Then we meant this guy, Jack, and their were like, gas mask zombies, and then we met some Slitheen again, and then…he – you – whatever, he died. Again. Regenerated."
"Go on."
"Yeah, um, so we did a bunch of stuff – slipped into a parallel universe, this universe, fought some Cybermen and went back home. A few months later they were these ghosts – and god, they were Cybermen and Daleks all at once and Pete came from the other universe for the Doctor's help and in the end I was trapped here. Without him."
Rose smiles. "You managed to project some message thing across a crack in the wall. I told you that I loved you. And then you disappeared."
She looks up again, and notes that the Doctor is significantly unnerved.
Laughingly, she tries to console him. "Aw, I'm sorry for blubberin' all over you. I mean, if we were having some contest over who has the most tragic relationship with other versions of ourselves, I mean, 'never-existed' sort of triumphs 'stuck in other universe,' don't cha think?"
"Rose."
He says her name like she's something almost forgotten, something so lost that it deserves to be savored. He sounds so old and broken and Rose wonders how the hell she ended up in this chip shop a universe or two away from her own.
Three years ago, she worked in a shop. She was probably gonna go from job to job till she found something that paid something half decent and marry Mickey and have a long, ignorant, human life. Instead, she's here, trapped like some dog on this Earth when all she wants to do is explore the stars.
Rose looks up once more, at those blue eyes and big ears, and can only think of how the man in front of her isn't the Doctor. He never took her to New Earth, never saved her from a scribble creature, and never said goodbye to her.
"I – I have to go," she utters, and bolts out of the shop.
0000
He walks back to the TARDIS, numb. He goes to Nargon II, saves an Imperial Princess, and then tumbles into 1961 and meets Marilyn Monroe. He zooms to New Earth, only because he hasn't been there in a few millennia, and meets the Face of Boe once again – whose nurse speaks of the prophecy of the Face of Boe's secret. The Doctor doesn't believe in prophecies, and finds himself back in the twenty-first century on earth. It's Tuesday, the twenty-first. One week from when he encountered the impossible.
He's planned to ask her if she wants to come with him. It's…wrong, he knows, but when he's with her…it feels right; almost if there is nothing wrong with the worlds, that the universe just might be in perfect balance.
But when the Doctor opens the TARDIS doors, there is no earth; merely the black curtain of space. He checks. Twice, thrice, and he's well past his seventh check of the coordinates when he accepts it. The TARDIS isn't malfunctioning. The TARDIS, in fact, is at the coordinates of where the Earth is supposed to be. It's the Earth that's moved.