It is Sasuke he teaches his Chidori, Naruto he teaches his philosophy, but it is Sakura he gives his legacy.

Team 7 meets at the bridge every morning for training which eventually just devolves into petty squabbles and when he can't take that anymore a D-Rank mission, maybe two if he's feeling vengeful. Sasuke and Naruto yell and throw punches and Sakura watches from the sidelines expressionless and with a calculating gleam in her eyes when she watches her teammates.

Good, he thinks because if he's going to teach the kid to take the missions he takes she'll need to know how to detach herself and look at her teammates as tools to be used, honed, and then used again.

He's not an idiot. He knows at the rate he's been going he is going to burn out his body or his chakra at some point, not soon, but he is never going to live to ripe old age. He had known that since he was a chunnin. He was born in a war time and during that time there was no sitting ideal there was only training to survive and surviving to train. So he rose through the ranks during a war and before he knew it the war was over but he was already an A-Rank shinobi by then and the village needed him.

So he went on more than his fair share of suicide missions, made ANBU, even made ANBU captain. Then when the Hokage knew he couldn't take it anymore he suspended him from ANBU and made him a Jounin sensei to a team that had always had too much riding on them to fail. So he figures if he already has students he's going to teach why not pick one and make sure that when he's old and, er, grayer someone's around to take the SS Missions he won't be able to.

Sasuke is already fucked up enough as it is, and if he has to do what Kakashi has done he would crack. Naruto sure has the determination but he's too goddamn likely to question a superior and get himself killed trying to be friendly. Sakura is a fangirl but she has smarts, even if she seems to not be able to use them around Sasuke, and apparently a hell-of-a uppercut if her sending Naruto flying is any indication.

So the second week of training he draws her away from the boys and tells her to meet him at training ground 24 tomorrow during team 7's off day and to not be late.

He can tell she is shocked the next day when he arrives at the training ground even before she did.

They progress from there. He shows her how to distance herself from a target, how to throw weapons with fractions of error measured in decimals, how to kill silently, how to track, how to survive. Then he takes her on a mission with the Hokage's permission- he shouldn't be surprised that Sarutobi caught on to what he was doing but for some reason he still is- and when she kills a child no older than 6 without flinching he knows he's created a monster, nevertheless a necessary one.

When he is 30 and recognizes a new entry in the Bingo Book under Haruno Sakura 'The Bloody Flower' he laughs because he knows he can retire now. After all, if there is someone there to take the missions he has been taking these last few years there is no reason to stick around.

When he is 40 and sees his former student coaching one of her new genin students how to kill with as much gore as possible because 'that's what the contractor wanted' he smiles.

Every village needs a ninja who is willing to take their morals and stomp the into the ground if it means completing a mission and it looks like he's finally succeeded in passing on that role to the next generation.