"Chidori relies on speed and a piercing thrust, so it demands exceptional eyesight.
"Reflexes can be trained, and even eyesight can be improved. But without a Sharingan, Chidori still falls a little short." Uchiha Yi wasn't making that up.
Eyesight could indeed be trained. The Fourth Raikage was every bit as fast as Uchiha Yi when Yi used Chidori, yet he could still react at those speeds.
But that kind of eyesight training had its limits.
Obito Uchiha's Sharingan solved that problem. You could say the Sharingan held Kakashi Hatake back. In terms of talent, Kakashi was at least the equal of Hatake Sakumo. With the right guidance, he might well become another Hiruzen Sarutobi.
Among ordinary ninja, Hiruzen Sarutobi was already one of the very best. Reaching his level would be an extraordinary achievement.
But the Sharingan weighed Kakashi down, and his state of mind became a problem. At the time when he should have been growing fastest, he let himself stagnate.
Of course, that Mangekyō Sharingan also raised the ceiling of what Kakashi could achieve.
Uchiha Yi was confident he could bring out Kakashi's potential even without Obito Uchiha's Mangekyō Sharingan.
Hashirama Senju's Cells Nutrient Serum, anyone?
Kakashi Hatake's battle instincts ranked among the best in the Shinobi World. If his physique and chakra reserves improved dramatically, his strength would grow before their eyes.
Kakashi Hatake frowned at the Chidori in Uchiha Yi's hand. He couldn't help marveling at Yi's chakra control. Yi could use an A-Rank Technique like this without hand seals. How terrifying was that?
My teacher really is unbeatable!
"But Kakashi, you aren't an Uchiha, and you don't have a Sharingan. Chidori isn't especially suited to you. So I modified it. The new technique keeps Chidori's piercing power without sacrificing much speed, and it's easier