A/N When Sasuke got curse-sealed, Kakashi just straight up applied a big-ass counter-seal. I'm assuming that means he's got fairly good sealing knowledge, if not quite mastery.
Beta'd as always by Bob Saget, who was a great help in getting Kakashi's particular brand of laziness right. Note this bit happens just before he propositions Sasuke about getting him his sharingan.
ooo
One week later
It was the end of the ninja workday, and the sun hung low in the sky above a red, traditional bridge. It was fast becoming habit for Team 7 to start and end the day on that bridge, their talks accompanied by the quiet sound of the water flowing over rocks and the soft waving of the bullrushes in the wind. Vivid blue dragonflies darted too and fro while a pure white heron waded in the shallows of the bend some fifty metres upstream, neck arched and ready to strike. Having spent the sunlight hours training and catching a surprisingly friendly Tora (still a tiger bloodlimit, quiet you), Hinata and Naruto had started on their way home while Tetsuo had stayed behind with their teacher.
"Hey Kakashi, you know sealing right?" He asked hopefully.
Kakashi slowly looked up from his book with an inscrutable look in his eye "Mmmm, I picked up a little here and there." He replied ambiguously.
"Could you look over my seals?" Tetsuo asked, sounding every inch the earnest student and holding out a well worn satchel holding a few different scrolls and notebooks. "Please?" He pleaded, attempting to look like a particularly hopeful orphan. It helped that he was currently both hopeful and parentless. "I've never been able to ask someone who actually knows what they're doing before."
Kakashi's shoulders slumped as he took one last longing look at his little orange book, before putting it away. In turn, he looked at the satchel with something that could be interpreted as dread. "Don't think I don't see what you're doing." Kakashi chided gently. "Well, I do need all my cute little genin physically intact." He mused aloud, carefully taking the satchel and unrolling the scroll holding Tetsuo's example large yield explosive tags.
He stared at it for a few seconds, before turning it sideways and frowning. Moving quickly he took out a small notebook and started making notes, then made an unhappy sound. He poofed out a clone which picked up a tag, walked to the far end of the nearby training field and created an earth hummock to sit behind, hiding the clone from view. A short while later the heated air from a sizeable explosion thwumped past. Kakashi frowned harder, and started writing more forcefully. This continued for several minutes as Tetsuo's anticipation built.
The wind sighed through the grass, the river burbled cheerily, the heron plunged its beak into the water. It came up with a struggling fish, which flapped desperately as it slowly ran out of oxygen.
Kakashi wrote.
Tetsuo waited.
"You have an idiot's luck." Kakashi stated flatly, finally breaking the silence.
"I... what?" Tetsuo replied, thrown off balance.
"This," Kakashi emphasised, holding up another example tag from the scroll, "Is not an explosive tag."
"But... it explodes?" Tetsuo asked hesitantly.
"An explosive tag is made of a chakra smoother, a compressor, a timer and an activator." Kakashi explained, as though reminding a child what what two plus two equalled. "This," he looked at the tag with the kind of scorn usually reserved for things that throw up on your rug, "is a compressor wielded to seven chakra loops. Where exactly have you been taking your inspiration from?"
"A book. I mean, it works like it said?" Tetsuo replied, wishing the earth would swallow him up.
"Did you not notice how inconsistent the timer was?" Kakashi asked.
"Nought point five to four second long fuse, randomly distributed." Tetsuo rapped out instantly. He might not understand his explosives, but he could still observe their effects.
"If you continue to use these you'll eventually charge one incorrectly and have it explode in your hand." Kakashi continued in an almost bored voice, though there was something below the boredom. "I'm frankly amazed that you haven't killed yourself - or anyone else - yet."
Tetsuo felt a rush of delayed adrenaline flow through his body, heating his limbs and a flushing his face a bright cherry red. He stared ahead dull eyed, breathing deeply. "Oh." he said, in a very small voice. Suddenly I am very glad that I never let Naruto use the large tags, he decided. Shit, I nearly killed one of my best chances to gain power... and myself... and an innocent kid.
"It is no secret," Kakashi began in what passed for a lecturing tone, "That only hacks who can't afford to make their money properly write books on sealing, and even then they don't include their best work. No-one with a shred of talent or a real understanding of the art would share any useful techniques that way, and the inherent personalisation of the art at all but the most basic levels makes it even more pointless. Most ninja children are aware of risks of unsupervised sealing by the time they join the academy." He eyed Tetsuo carefully, the silent question obvious. Or possibly he had missed lunch.
"Ah, well, I never spent much time with the other children at the orphanage." Tetsuo scratched the back of his head. "They were kind of boring?"
Kakashi just looked at him.
"So... uh?" Tetsuo rallied magnificently. Truly, his articulate and thoughtful response was a wonder for the ages. A triumph of intellect not seen before or since. Nor - strictly speaking - during.
His teacher stared at him for a long moment, then glanced down at his orange book longingly. "I suppose I'll have to find someone to teach you the basics, if only to stop you blowing yourself up." He allowed grudgingly.
Tetsuo's eyes lit up. "Yessssssssssss."
"Only the basics." Kakashi warned, but his young charge was no longer listening.
"Sealing! Sealing! Sealing! Hoy!"
