Jiraiya

Kakashi's special training for Sasuke gradually got on track. Since Sasuke himself had Lightning Release, it saved Kakashi quite a bit of trouble.

Next, he needed to teach Sasuke how to properly use Lightning Release Chakra, fully utilizing its characteristics to stimulate his body and greatly improve his physical abilities—especially his speed.

In addition, Kakashi had to teach Sasuke how to properly use the Sharingan. Since the Uchiha Clan had been wiped out and Sasuke had been too young at the time, he had no idea how to use his own Sharingan. In all of Konoha, the only person who understood how to use the Sharingan was surprisingly Kakashi, a non-Uchiha Clan member.

Shimura Danzo knew how to use it too, of course, but that old man hid himself well. Even now, no one knew that he had collected a whole pile of Sharingan.

After laying all that groundwork, Kakashi officially began teaching Sasuke the Lightning Release Ninjutsu known as Chidori.

Kakashi, famous throughout the ninja world as the Copy Ninja, had created only one ninjutsu of his own: Chidori. Its power was tremendous, and the deafening sound like countless birds chirping at once, along with the blinding flash of light, deeply attracted Naruto, who loved showing off.

Naturally, Naruto clamored to learn it too.

Kakashi did not refuse. Since all the students were there anyway, he simply taught them together.

Unfortunately, even Sakura Haruno, who was only watching for fun, understood some of the principles. Sasuke had already successfully condensed a small amount of Lightning Release Chakra in his hand, while Naruto was still scratching his head with a constipated expression.

In the original story, Naruto had also asked Kakashi about the principles behind Chidori. Kakashi had not held anything back, yet Naruto still failed to learn the technique.