Author's Note: This is AU, in the idea that Kakuzu didn't die fighting Naruto and Kakashi.
The first thing Hidan had done after getting out of that godforsaken hole was to breathe—well, specifically it had been to hack a chunk of half-swallowed clay out of his esophagus and then cough for ten or fifteen minutes, and spit up grains of dirt.
Oh, but then! He'd taken the biggest gulp of air he'd probably ever taken in his entire life, sucked the precious oxygen in and savored it, forcing what was left of his throat to pass air through over and over even though it hurt like hell and there were still all kinds of things lodged in there that scratched and stabbed, but Jashin did it feel good to just breathe again!
Kakuzu, of course, had to ruin his fun and start complaining about how long it took him to dig Hidan up with only his two arms, since all of his hearts had been destroyed but one, and didn't the use of any of his beasts.
"Hurry up and sew me back together!" Hidan had demanded the second Kakuzu picked him up by the hair. "There's some weird shit crawling around in me, and I want it out now!"
"I've been at this for two days," Kakuzu said flatly, and he sat Hidan down on a rock, and left him there while he proceeded to take a nap, which no amount of yelling could rouse him from. Hidan, who had already spent the past forty-eight hours in the ground, didn't want to wait any longer than he already had to get put back in order, but Kakuzu was the only one who could fix him and if his lazy ass was asleep, Hidan had no choice but to sit for another six hours until Kakuzu was rested enough to begin the process of turning the puzzle that was Hidan back into a complete picture.
It might have been easier, had that Nara brat not blasted him into bits. Kakuzu spent half a day scouring through dirt and mud for missing pieces of Hidan, finding fingers, toes, organ bits and bones in all sorts of places. It wasn't until sunrise the next morning that he was positive he found them all, but this was only the beginning.
For one, Hidan had been exploded. The edges of his flesh—even where they had begun to heal—were ragged and burned making them hard to connect. Not only that, but because he'd been so thoroughly torn asunder his insides had been left open to the elements, and so even before the sewing could begin Kakuzu had to clean him out, flush away the dirt and bugs and even some small plants that had begun to take root deep in between his muscles. It was like hemming a shirt and tending a garden at the same time.
And two, once Hidan was back together, he couldn't be moved. They were stuck in the forest for nearly a week, vulnerable, tired, and unprepared. Hidan's bitching was unceasing, and Kakuzu got sick of hearing it after a while so when Hidan finally fell asleep he sewed his mouth shut—needless to say, the alarm and fury on his face the next morning was priceless: not a title often given by a man so consumed by greed, and it was almost worth all the work just to see him so pissed with no way to retaliate.
"I suppose you'll try to get me back for that after you've healed," he said some time later, when Hidan had quieted down. The zealot had gone mysteriously still, the only sound or motion his constant, heavy breathing through his nose. When Kakuzu spoke he didn't look at him, but he mumbled something that sounded an awful lot like You bet your ugly ass I will. Kakuzu nodded politely, and went to stand over his incapacitated partner, and folded his arms across his tan chest riddled with hundreds of stitches. "Well, since that's the case, you ought to know something before you get any stupid ideas in that imbecilic head of yours." He crouched down, so that they could see eye-to-eye. They were close enough to kiss. With a hand still crusted with dried mud, Kakuzu patted Hidan's pale cheek, almost fondly, and smiled. "Just remember, I didn't have to dig you up. I could have left you here for all eternity. Can you imagine that, Hidan? Hundreds and hundreds of years, never rotting, just lying there buried under the dirt, breathing it in while all kinds of other life chewed their way into you to make nests and breed? That could have been you life, until the end of all time."
Hidan didn't say a word. He stared up at Kakuzu with silently pleading eyes, as if to say, No. Anything but that. The look of total mortification was enough for Kakuzu, and he pat Hidan one more time, still smiling, and sauntered back to where he'd been sitting before. Later that night, when Hidan was asleep again, Kakuzu took the stitch out of his mouth.
They left the woods the next day. Kakuzu made no comment on it, but Hidan had picked up two new habits. He'd started breathing more frequently than he ever had before, which was mildly annoying and very disturbing, but his other habit was so hilarious that Kakuzu could forgive the other.
From that day on, Hidan never spoke first in a conversation, and he never did get Kakuzu back for sewing his lips shut.