It started with a question. (There were things that led up to the question, but the question was a definite starting point for something.)
"If you could go back in time, theoretically, would you? Even if you couldn't change anything, and you had to watch them die again? Even if you made everything worse?"
Bitter laughter. So out of place coming from its source. (Everything was out of place. Random, dirty rags that should have been a stupid, stupidly bright orange. Smooth skin where there should have been scars. Red eyes where there should have been blue. Fangs. A bitter glint in eyes that used to be shining with joy or determination, or, if nothing else, passion.) "Oh, Shikamaru, please don't ask me something like that." Silence. The clouds, free of the weight of responsibilities and memories Shikamaru carried, floated on ahead. Then, "I would do anything to see them again…"
"Would you even kill me for that?"
Silence, again. A whisper. "Sorry, Shikamaru, but I guess I'm a little too selfish."
"It's alright." He closed his eyes. Cloud-watching was tinged with bitterness these days. (If he was like a cloud, as he'd so often wished before, the weight of everything he'd seen and done would overload him and every tear he had would just flood out. Wouldn't stop, until he had nothing left.
(Already had.) "I think I'd do the same. Even if it was only for, maybe not five minutes, but two hours… I wouldn't do it for anything else, you know that, but for them…"
"I know, Shikamaru, believe me. I know."
They studied with fervour, putting together both of their great minds and, although they both detested any kind of paperwork with a passion, scribbled down many notes and equations. Re-scribbled, because when Shikamaru put everything into something, it had to come out right. Had to be perfect. Especially this.
Seals were designed, or borrowed from elsewhere and applied in a different manner. They were put together in one large array, scrapped, and redone. The scrapped paper was kept for reference, when it would've been easier to use it as fuel for a fire.
They kept moving during this time, across nations, but the thought of being caught wasn't as high on their priorities list any more. Clones had to be made to carry the amount of paper they brought everywhere. Once, when hunter-nin came after them, they had to jump into the water to escape. Most of the paper was saved, but some was lost – and redone, even though they weren't even the ones they'd currently been working on.
(Naruto also wrote a terrible porn novel during this time, though Shikamaru figured that it could've been popular had they been able to publish it. It saved their lives, or at least made it a lot easier, when they proved to the authorities they were just ordinary citizens who were also budding writers, and reciting a certain passage about five lovers' night time activities was effective in knocking people out. It was then that Shikamaru wondered if Oiroke no Jutsu might've been more practical than it first seemed.)
Breakthroughs were made. Sometimes, proven false.
They ate little, slept less. It didn't matter any more. They'd found a way, or thought (hoped) they did.
At one point, they ran out of ink in the middle of figuring out something important. A couple of hunter-nin squads were slaughtered, and their writing was in red-turned-brown for a time. It didn't matter at the time, and they forgot soon after.
(The pens and paper were, of course, stolen. Just like everything else.)
When they were on the verge of solving one major problem, they had to make a decision. Who would have the chance to see everyone again? There could only be one. And, if it failed, probably even if it succeeded, the other would have to live alone. Probably couldn't.
The jutsu could only send one back (in incorporeal form, only, but surely that was better, easier), and even if it could send more, there needed to be someone to perform the jutsu on the ones who'd get their second chance. When they argued over who would do what, the conflict was mostly internal. Would they leave the other, and always have the terrible, terrible knowledge that the other man was left behind? Or would they give up their chance to see their loved ones again?
(Or they could both stay, and give up the chance to see them but still have each other. But that would require moving on, so neither of them ever voiced this thought, if it ever even occurred to them.)
But really, there was only one answer.
"I've got another soul within me," Naruto pointed out quietly, looking away. "I'm the only one with enough chakra to do it. Besides, we need knowledge and strategy to succeed, which you've got in spades, and I don't think I could bring back all of my power with me. I'd be pretty useless, compared to you."
Shikamaru couldn't argue. He didn't even know if he wanted to.
That night, he saw Naruto put a kunai away somewhere safe, but not somewhere that it could easily be reached in battle. They didn't have many – not nearly enough weapons, not nearly enough anything – but Shikamaru didn't take long to figure out what it was for, or what it probably could and would be used for.
He didn't want Naruto to kill himself afterwards, whether they succeeded or failed. They'd already figured out that no matter what, the jutsu user would be left alone or else dead. But he didn't know which was worse.
(He had a good idea, though, and he found he really couldn't blame his friend no matter how much he wanted to scream at him.)
"Are you ready?" Naruto's skin seemed to glow red. Shikamaru swallowed, and nodded. Naruto closed his eyes and made a hand seal. Four clones popped into existence and stepped in their designated circles. The real Naruto did the same, forming a pentagon around Shikamaru. In unison the Narutos flipped through a series of hand seals.
Shikamaru wasn't sure why he felt so nervous. All he had to do was stand back and relax; Naruto would be doing all the work, and Shikamaru trusted Naruto to do it right. But what if he was standing a bit off from the very middle, and only part of his body or soul was sent back? What if it absolutely required him to relax, and he wasn't doing it well enough? Practically, these worries made no sense, but they raced through Shikamaru's mind nonetheless.
What if it didn't work, and Naruto was left behind by himself?
What if it did, and Shikamaru screwed up his part of their mission?
The array of seals around them flashed, filling Shikamaru's vision with whitish-blue light. He squeezed his eyes shut, but it pierced through his eyelids. The seals in which chakra was stored released the chakra into the seal around him, controlled expertly by Naruto, or at least that was what was supposed to happen. He wasn't sure, because all he knew was that the light was getting brighter, unbearably so. He heard a worried cry and he wasn't sure if it was him or Naruto who yelled, "Don't stop!" or even someone else. He didn't remember falling, but he felt his body hit something solid and the rough hard stone against his cheek, and there was pressure on his shoulder and a pair of red eyes stared into his own and everything was spinning and then it was gone.
Oiroke no Jutsu: Sexy Technique