Hello, everybody; ModernDayBard here! This one's a little trickier for me to write, but I'm gonna give it my best shot.
Disclaimer: I don't own Marvel, or anything they own that appears below. I don't even work for them. The only thing I do own are the words I used—I'd say the ideas, but these are probably what-if's that many other fans likewise imagined their own versions of.

Chapter 3: Family

This was wrong.

He could scan the field around him on this strange new planet and see people he didn't really know, but who had fought beside him, start to crumble away into ashes, or dust, or whatever-it-was. These were strong people, fierce fighters, but even they were not strong enough to stay.

Trembling with fear and confusion, the teen turned to the strongest person he knew, and the one person he knew well on this world, seeking some kind of answer, some kind of reassurance that as wrong as things looked right now, they'd get better—that their band of allies would actually win, or better yet, that he was asleep on the ship and dreaming up a nightmare future scenario.

Instead, it got worse.

Rocket was only a yard or so away from him—just at the other end of the log Teen Groot had slumped against when his legs gave out in shock at the destruction around him, when the army began to literally dissolve—but the distance may as well have been a mile or more for all that the grey-furred creature could cross it with his legs already beginning to turn to ash.

Every drop of sap in the young tree's body burned to spring upright and run over to Rocket, to anchor him somehow and keep him here, but he couldn't move. His wood was frozen in horror as the other Guardian continued to disappear.

Rocket must have seen the fear in the teen's dark eyes, because he tried to hide a little of his own, tried to show as gentle a smile as he could manage. "Easy, buddy. Quill's comin'—just hang on…"

Groot, whatever his age, was a tree of extremely few words (3-5, depending on which Guardian you asked), but as Rocket was almost gone, he found one more, and in came out in an anguished wail: "DAD!"

He just saw Rocket's ears shoot straight upright and eyes widen before they vanished, and he managed to propel himself forward, finally—

But too late.

"Dad! Dad! DAD!" He kept screaming it, kept staring at the place Rocket had been, hiccupping and wailing in anguished grief. Rocket couldn't be gone—he was tougher than anyone he knew. All the Guardians were, but Rocket was…well, Rocket. He was short, but he stood tall, talked big, carried a big gun, and tried to hide an even bigger heart. Surely he couldn't just be gone?

Groot never could say later how long he was there, crying out in grief (sometimes his new word, sometimes a wordless scream), passed by the surviving warriors of this strange land. Some gave him odd looks, others expressions of grief that mirrored his own, and some were so hollowed out by lost they had no expression at all, but he ignored them all.

"Hey, uh—Groot, was it?"

The young tree turned his head slightly, seeing the man who now stood next to him. At first he didn't recognize…Oh, yes, he did. It was the man who'd introduced himself in the middle of the fight when he had tried to say, 'pleased to meet you'. It wasn't as bad a mistranslation as many, but he doubted this man could understand him at all…

It struck Groot then that there was a strong possibility no one on earth could—Quill'd had to learn, along with everyone else, and this was his home planet—and he began to feel even smaller than a twig as he realized just how alone he was on this strange world.

"Dad," he croaked out, in a voice torn and small by all the torment he'd put it through in his grief, and he indicated the spot he was crouched over, where Rocket had been. Where Rocket should be.

The man—Steve Rogers, hadn't he said?—closed his eyes for a second, and Groot read the exhaustion there, but the grief as well. Well, if half the universe had just been wiped out, this man had likely lost someone as well—perhaps just had his own version of the nightmare scene Groot had lived through. He opened his eyes, lay a hand on the teen's shoulder—a hand not so much comforting as heavy with a shared grief—and mercifully, didn't speak.

There were no words, anyway, but Groot didn't want to have to play through the too-familiar scene of someone finding out about the 'Groot' language. Particularly when there was no one who could translate—

Wait.

Wasn't there?

Or was he gone, too?

Groot really didn't want to think about that possibility, and he forced himself to his feet, already looking around for the one other face that would be familiar. The man beside him put out a steadying hand, and didn't even flinch when it came in contact with the bark-like texture of the teen's arm.

"Easy, there. You good?"

He didn't answer. It wasn't the deliberate rudeness he'd been exploring as he entered the teenage phase of his life-cycle, it was a single-minded focus: the only thing holding him together at the moment. Quill and the others were coming—Rocket had said so—and until they got there, he'd stick by the one other person he knew for sure would understand him.

He saw him, then: standing with his new axe hanging limply in his hand (Groot unconsciously rubbed his new arm at the sight of its handle), surrounded by some other individuals he supposed were the 'Avengers' this Thor had told him about. The blonde lady saw him first, and as her eyes widened, Thor turned.

"Ah, friend Tree. Thank you Rogers, for finding him." Thor was no longer trying to sound cheerful, as he had on the ship, and given what had just happened, Groot was glad.

"Dad," he croaked again, pointing back the way he'd come, to where Rocket had faded. Then, indicating the blue sky above them: "I am Groot."

He ignored the confused looks from the others gathered, focused on Thor who closed the distance between them, resting a large hand on the tree's thin shoulders. "Of course they are coming. Family—" his voice broke there a little, but he recovered and pressed on with another forced smile, a small one, now, "Family always comes back for its own. They won't leave you behind."

Content, Groot nodded, then sat down beside Thor and tilted his head up, watching and waiting, ignoring the others around him and their murmured conversation. At some point, Thor must've explained who he was, why he was there, and who he was waiting for, because the looks darted in his direction changed from confused to sympathetic, but he didn't care. He kept looking up, kept waiting.

"Easy, buddy. Quill's comin'—just hang on…"

Right now, that was all he could do.

He was the first to see the Milano appear outside the barrier—early the next morning. He lurched away from Thor (who he'd been shadowing the whole time) and began to run towards the blue-and-orange ship just as the alarm sirens started wailing.

He vaguely heard Thor behind him shouting reassurances that he knew this ship, that it was friendly, but he didn't care about that, right now. His family was here. He needed them so much, right now: He needed Drax's simple honesty, Mantis' gentle innocence, Quill's confidence, and, most of all, Gamora's kindness. He needed them so much.

A portion of the barrier opened right in front of him and he ran through it just as the ramp lowered. Groot didn't stop running until he saw who the first figure off the ship was, then he halted in confusion.

Nebula?

He tried to shake off any misgivings. After all, the group had been chasing after Thanos, right? Of course they'd encounter Nebula as she pursued her own mission of vengeance, and surely Gamora could've convinced her to join forces with them.

Then she caught sight of him, and that expression of emptiness, the too-familiar look of someone who's been carved hollow by loss, by grief, brought back all the fears he'd tried to shake. Gamora, gone too? Nothing else could make Nebula look at him like that. He began to shake again.

"Groot, where's Rocket?" Her voice was flat, like she was barely managing to keep herself pressing forward.

Mechanically, he pointed to where Rocket had last been and croaked out, "Dad."

Nebula hadn't always been able to understand his words, but this time, at least, his tone made it clear. "Damn."

That about summed it up. Then she turned to him again, and the realization he saw dawn in her eyes made the world fall apart again.

No, it couldn't be—he couldn't be the only one left. That couldn't be what she meant with that expression. They couldn't be gone.

He tried to run past her into the ship—into his home—but she intercepted him, wrapping him in those metal arms, though whether she was just trying to stop him, or shield him from the emptiness inside, or even pass on a modicum of comfort, he couldn't say and didn't care to know. He tried to squirm out of her grasp, but the blue cyborg was too strong from the grief-stricken tree.

Drax, with his plain-spoken, literal words and unshakable loyalty, gone? Mantis, with her wide-eyed curiosity, her love for life and new friends, gone? Gamora, with her fierce protectiveness, but gentle touch and warm smile, gone? Quill, with his snark, his jokes, his music, his references nobody but he understood, and his heart (however much he tried to play the rogue and outlaw), gone?

He continued struggling in Nebula's grasp, desperate that she was wrong, even that she was playing a cruel trick and that his family was just in there, just out of his sight.

"WE ARE GROOT!" he screamed, and then, he couldn't stop: "WE ARE GROOT, WE ARE GROOT, WE ARE GROOT!"

There were voices behind him—maybe even Thor's—and Nebula's quiet sobs in his ear, but he couldn't make himself focus on them, couldn't make himself care.

This was wrong.

He was alone.

So, yeah. Double-punch of sad with this one, but even in normal-movie cannon, I always figured it was kind of a one-two punch, even if we never actually got to see Rocket realizing he's the only Guardian left. I had to put Groot realizing it, I couldn't not, even though it broke my heart to write.
It's odd, as I said in the beginning, I expected to have a lot of trouble writing this one, since I really didn't have any of it even half-written in my head, like I did with the others, but once I sat down, it just came so easily, I got it all out in a single sitting. And yes, as said before, each one-shot is its own AU, so Thor is alive in this one, instead of Loki, unlike in the first. It's just simpler that way for me. Plus, I honestly can't picture the Guardians getting to earth if they don't encounter Thor (at least not without some major coincidence/Deus-Ex-Machina's).
As always, if you saw something you liked, or something you think I can fix/improve on for next time, don't hesitate to leave a review and let me know!