Because it's an almost irresistible episode to play with: the end meeting the beginning;
because it's already been done amazingly well more than once, but (that I've found) it hasn't been done backwards;
and, mostly, because I wanted to read it...
...a move into a slightly AU storyline, although, in the end, it doesn't really matter.

Fragment

"Not bad for a flyboy," she teased, coming up behind him.

She realized her mistake before he ever turned, feeling the differences in his body language, a particular tension that she had almost forgotten about him. It gave her the briefest moment to prepare herself for the reaction that she then knew would follow: not long enough to stop her gut from twisting and a wave of nausea from rising.

"Have a lot of experience with 'flyboys', do you, Torres?" Paris returned, his face a mask that she had once interpreted as arrogance, his tone suggestive, almost leering. Her eyes went to his collar, wondering just how large of an error she had made and found nothing. No pips. No rank. Not yet reinstated as a Lieutenant or even as a pilot.

Just Thomas Eugene Paris, inmate of the Federation Penitentiary in Auckland, New Zealand. On temporary release and signed on to rat out his former Maquis shipmates. Including her.

Hell.

She rallied for defenses that had once been automatic, and a second tide of nausea washed through as she realized just how vulnerable she had become. She looked to the young man at his side for an out, but a newly minted Ensign Kim looked back at her without recognition, though with more than a little trepidation.

Play the game, Torres.

"Enough to know the type," she quipped back, crossing her arms for effect, careful to tuck her ringed left hand under her right arm. Then quirking an eyebrow and a corner of her mouth, she added, "Still, that was a nice leap the two of you made."

He relaxed just a touch at that, not least, she knew, for her pulling Harry into her compliment. The mask didn't drop, but the slightest glint flashed through his eyes and damn but he looked good.

And then she noticed the other differences – the thinner frame, the thicker hairline. He was, she realized belatedly, a couple of years younger than she was. Her mind played with that for a moment before reinforcing that this was not yet her Tom.

But he would be.

It was as inevitable as it was incomprehensible. And standing there before Tom in all his defensive, closed off glory, she realized again how lucky they had been. Were. Would be.

The ring encircling her finger warmed in its place under her arm.

Harry, apparently feeling that the tension of the situation had abated somewhat, ventured into the conversation. "I don't think we've met – I'm Ensign Harry Kim, operations officer." His eyes flitted over her gold uniform, took in the provisional rank bar. "Um, sir."

Well there's a first time for everything. "At ease, Harry," and she was actually laughing. "B'Elanna Torres." She offered her hand and then, seeing Tom also puzzling out the uniform and rank, she added, "Chief Engineer," and smirked at the pair of reactions. To hell with the Temporal Prime Directive.

"But..." Harry frowned, thoroughly confused.

"Chief Engineer, eh?" She could practically see Tom's mind working through the implications. His appreciative grin almost managed to touch his eyes. "It must have been a hell of a ride."

"You could say that," she agreed, her arms relaxing to her sides.

Tom's expression shifted, his eyes following the glint on her left hand.

"Nobody wears rings anymore."
"Nobody has a television in their living room either."
"Well you're not wrong there."
"Humor me?"
"Make it worth my while?"

Then the mask did drop, and his eyes met hers. Again, she watched as he fit the pieces together – her greeting and response, the uniform, the ring. Intuition and instinct did the rest.

"A hell of a ride indeed," he intoned.

She didn't bother to deny it.

Harry and Seven of Nine stepped into the turbolift with Icheb and Naomi. B'Elanna moved to join them and then felt the hand, light but insistent on her arm. "Take the next one with me?"

His eyes held her with that intense look that he knew (or would know) she couldn't resist. She nodded, letting the lift door close.

"When?" he asked, once they were alone.

"The ring?"

"The ring. The beginning. Everything."

"I don't think we have time for everything."

The lift doors reopened and they stepped inside.

"B'Elanna..." And she heard the desperation and the need and remembered where...when...what he was.

"You won't remember."

"I know." But his eyes met hers again with naked longing, though not for her. Not yet.

He wasn't hers, but she couldn't deny him what he needed. Even if only for the few minutes before they would both forget all of this.

"I'm honestly not sure when it began," she told him. "I don't think either of us really knew." She touched the ring on her hand. "This is new though, a couple months back." She recalculated. "About six years forward for you."

"Six years, huh?" His smile was soft, his look almost sheepish. "Slow played it there, I guess?"

She smiled back at him. "A bit." She let him off the hook: "We both had some growing up to do."

At last, the smile made its way fully into his eyes which locked on hers. He drew in a slow breath and lifted a hand to graze her hair. "Still, I was – will be – an idiot."

"Likely," she agreed out of habit, but her attention was on those eyes and the feel of his hand hovering near her head and how suddenly close his warmth felt in the confines of the turbolift.

Then he frowned, considering. "And the rest?" he asked as if compelled.

"Better than you can imagine," she assured softly and watched the rest of the tension finally relax away, and she ached for him. "I wish you could remember some of this."

He shook his head, the smile returning. "I have some growing up to do first, remember? And I don't think I'd want to risk any of it."

Gods, that soft smile and those damnable blue eyes. "Tom..."

When their lips met neither knew who had moved forward. Utter familiarity met utter newness in her mind at a kiss that both was and so definitely was not the first. For a long minute, it deepened and then he ended it gently, holding her close, bending down to touch his forehead to her own.

They separated as the lift doors opened at his deck. He stepped away looking younger than she had ever seen him, his face unshuttered, his posture easy. Her breath caught as he looked back with that uninhibited, exuberant expression that would not reappear for how many months? a year? and threw her a wink.

"See you on the other side, Torres."