Kakashi may have only been a child, but he is a genius, so he knows that he should follow the rules set by the man who made the technique. It's only later that Kakashi finds out why. Minato-sensei failed to follow his own rules, and that really annoying foreign woman who can't ever shut up saw him do it.
Of course, because that Uzumaki woman can't shut up, soon the whole of Konoha knows that for some reason, she has to marry Minato. At first, no one really believed her, because she's loud, and foreign, and jeez, what's with all this declaration making? Kakashi is worried that Gai's getting a little too infatuated and that he might get weird ideas. But Minato-sensei only confirms her complaints, and he takes Kakashi aside and explains just why.
Kakashi thinks maybe Minato-sensei is pretty stupid if he thinks Kakashi doesn't know better. 'Accidentally' Gamabunta's over-sized ass. Kakashi isn't a genius jounin for nothing. But he takes the warning to heart. Who would want to have some girl forced on them, anyway? Certainly not Kakashi.
And years and years after Konoha barely survives that Uzumaki woman's fury and the Hokage tower has been rebuilt at least three times and Minato-sensei's apartment block five times; years after that, Kakashi is looking down at a whiskered face and explaining about Minato-sensei's special Ultimate Winning Technique.
"Now, listen closely," he said sternly. "This is a very dangerous technique" -- and Naruto had blinked those big blue eyes with a jaw lose with trepidation, reminding Kakashi that Naruto might be fifteen, but he's still pretty much a kid -- "One that the Yodaime himself created and helped him become a jounin. Only two people know how to do this technique, and the other is me. Before I teach you, however, you must promise that no one will ever see you practice this technique."
"Eh? Why?" he demanded, giving Kakashi suspicious looks, as if this technique might be some variation of his Sexy or Harem no Jutsu.
Kakashi leaned back and scratched his cheek with one finger. "Well, the Yondaime was never sure why, but the first person to see you perform this technique pretty much has to become your romantic partner. The world conspires against the user and the victim and throws them into romantic situations." He paused for a moment, remembering that mess. "The Yondaime once came back from a mission that shouldn't have even bruised him, but he was really beat up. Jiraiya called it the hurt-comfort scenario."
Naruto gagged, and Kakashi smiled vaguely. Back then, Jiraiya's hurt-comfort scenarios weren't quite so ... adult oriented. His books have dropped into perversion the last five books or so, but they used to be romance, and Kakashi remembers that the first had actually started out pretty serious.
Of course, even that one had graphic sex-scenes, but at least it had mostly been serious. Kakashi pondered the possibility of his childhood being destroyed by Minato-sensei's master, and thought it was pretty likely.
Kakashi has only used this technique once, and that was to get the Mangekyo Sharingan. He made utter certain -- the way only a paranoid genius nin with the Sharingan eye can make certain -- that no one had been within miles of him when he did it. When Naruto ask if anyone has seen Kakashi do it, he can honestly say, "No," because otherwise the jutsu would have already made them show themselves if someone had.
A few weeks later, he's starting to have his doubts about teaching Naruto that technique. It had sort of been his present to help Naruto vault into the Hokage's seat, but Naruto has got that sneaky contemplative look, and when he forgets himself and chuckles, the sound is positively evil. He must be working on his own versions again; whether or not it would surpass Konohamaru's special Combo of the Sexy No Jutsu was only to be seen.
But even when he hasn't set foot in Konoha in three or four years, Sasuke has a sort of ability to disrupt Naruto's plans. Tsunada has information that implies that they have to move now if they want to get another chance at retrieving the Uchiha. Sasuke is, of course, more powerful every time they catch up with him, and within minutes, the situation is desperate. Kakashi is being careful to keep up with Naruto, because he wants to do what little damage control he could in Naruto starts to surrender to Kyuubi as he's so prone to doing these days, or decides to use whatever weird technique he came up with.
Which would explain why Kakashi and Naruto are hiding behind some trees while Naruto figures out how he wants to do this. Kakashi's genius is wasted, because he's so pissed at Sasuke over this entire thing that he just wants to assassinate him, and retrieving missing nin was never Kakashi's deal anyway. Naruto gets a determined look on his face, eyes shot with the warning blood-red of Kyuubi's fury, and Kakashi watches him cautiously. He really isn't thinking about much more than the fact that if they could just kill Sasuke, this would be so much easier, and that was why he didn't really recognize the seals Naruto is flipping through until it's too late.
Because Kakashi might be a genius with a memory like a steel-wire trap on a feather's weight trigger, he's never actually seen Gary Stu no Jutsu performed. He has time to think, Oh wait -- shit. Then he gets two eyes full of Gary Stu no Jutsu Naruto.
There aren't really words. There aren't images that could accurately convey the concept of Gary Stu no Naruto. Mental images pale in comparison, and memories are like old faded photographs. Naruto doesn't really look different, the logical part of Kakashi's brain gibbers, he looks exactly the same, but he's changed.
Which makes it so utterly and unhappily clear to Kakashi that no one has ever seen Naruto perform this technique before. Its perfectly obvious to a genius jounin like Kakashi that he's under the influence of a jutsu, and it makes his ANBU side -- that usually sat silently in a corner being creepy and still -- burst into tears.
Kakashi has mysteriously rediscovered his sex drive. He just might kill himself.
While Naruto lunged around the trees to beat the crap out of Sasuke -- and Kakashi has no doubt he'll succeed, but he isn't sure if that's an unbiased thought or not anymore -- Kakashi just sort of curled up into a fetal position. He'll come out and join the world again in about a thousand years, maybe.
Well, he kind of had to beat some sense into Naruto's head, so maybe he can't hide out for that long. He does wait until everyone is ready to go before reappearing, though. So when the team breaks for camp, with Sasuke's unconscious body left to the elements because they're all really pissed at him, Kakashi calmly eats his travel rations and listens idly to the mantra of logic verses the stupid jutsu.
It went something like this:
'It's probably no use fighting it. Let's just go with it,' the Addled part of his brain said.
'That's just the jutsu talking,' the Logical voice said dismissively.
'So? What if it doesn't wear off, huh? Besides, as Naruto's teacher ... as one of them, anyway, it's it our duty to teach him? We know a lot, with all those missions and reading Icha icha!'
'Jiraiya couldn't write an accurate sex scene to save his life, and you know it. And for our health, let's not. Naruto is a kid.'
'Naruto is a teen with probably a healthy interest in sex!'
'With women. Besides, it would be informative to see if this wears off in time.'
'You don't remember anything, do you? Uzumaki tried the same thing, it didn't work. And I missed that whole 'having sex' jig!'
Kakashi's ANBU side stopped crying long enough to stun both voices into silence. Kakashi always had liked his ANBU side. Of course, had Logic still been capable of it, it would have questioned the possibility of his inner voices being able to attack each other without words, and the level of sanity implied by the fact that Kakashi's inner voices didn't like each other.
Kakashi might have replied that he was a genius nin, and Logic didn't have to worry about him following it's rules.
The next day, while they're walking, Kakashi twists an ankle, and decides that a kunai in the heart sounds just about right. The others are in awe of a jounin twisting their ankle over a nonexistent rock, and Kakashi starts looking for sharp edges. Unfortunately, two things occur. The first is that he realized he used all of those a few days ago while tracking Sasuke and during the fight, and the second is that Naruto suggests the others keep going while he deals with Kakashi.
Kakashi knows what's coming. Sakura had bandaged his stupid ankle, and then announced that his chakra was all sorts of fucked up. Kakashi didn't even need to see the sudden look of comprehension that appeared on the blond's face.
"U-um," Naruto stuttered uncertainly.
Kakashi sighed and slouched slightly. "Don't worry about it," he said, waving it off. "It didn't work." Because even after all these years, he's a terrible liar, but Naruto might be in the mood to ignore that.
"It didn't?" he asked, frowning. "But -- but I used it, and I know Sakura saw me during the fight, and she's not acting funny -- and are you sure it's not working?"
Oh, it's working alright. But -- "Naruto, did you take that into consideration when you used that technique?" he inquired mildly. "That Sakura would see you, so you sort of accidentally forgot to warn me about what you were using?"
Naruto sputters and mutters and grumbles and turns guilty blue eyes to the ground. Oh, jeez. "U-um, well, y-yes, but no, not really, but see, I um ... Well, I didn't want it working on Sakura! Or Sasuke -- bletch!"
And if it were anyone else, or perhaps if it wasn't for the jutsu, Kakashi would have punched him in the face. Instead, he scratches his cheek with as mild of an expression as he can manage. That last part of Naruto's sentence rang true, but he's not a genius jounin for nothing. There's more to the story than that. His ANBU side smells blood in the water. "Naruto, you didn't ... want this to happen? Did you?"
Naruto turns a telling shade of red. "U-um."
Jeez, of all the things to inherit from Minato-sensei! Doing that on 'accident'! Kakashi considers this for a while. Then, spitefully, he uses deadly speed and pulls off his own transformation.
Naruto swoons. Kakashi figures it won't hurt to let Naruto's head bounce off the ground a few times. "We'll see how you like it," he said pleasantly, and wonders if maybe Naruto's mother would have done the same if she could have.
Probably. He certainly sympathizes with her desire to destroy Hokage tower.
Instead, he thinks that maybe he'll go play Janken with Gai. Konohagakure could always use a moat.
-- THE END --