Katakuri clearly understood his mother's nature well. He knew Charlotte Linlin was an exceedingly cold and brutal person, selfish to the extreme.
To her, her children were nothing more than tools. There was no real familial affection to speak of.
Seeing this, Sarutobi Hiruzen did not beat around the bush and said directly, "I heard your Observation Haki can see the future,"
"And that you're a good teacher."
Sarutobi Hiruzen's goal was naturally that future-seeing Observation Haki.
Although he knew such a thing depended on talent and that not everyone was Monkey D. Luffy, he still wanted to give it a try.
"I need you to teach me your ability to see the future."
Katakuri was somewhat confused. Since when had he become a good teacher?
Katakuri clearly did not mind teaching his Observation Haki, but to be safe, he said in advance, "The ability to see the future isn't something everyone can learn,"
"I can't guarantee that you'll master it."
Sarutobi Hiruzen naturally understood.
"You teach first. Whether I can learn it is my concern."
After teaching him the future-seeing Observation Haki, Katakuri was taken away. In return, he and his siblings would be given a relatively free environment.
"As expected, it wasn't that easy..."
Sarutobi Hiruzen wore a trace of unsurprised disappointment.
Katakuri had taught him for quite some time, but most of it was merely the sensation of seeing the future and the process of awakening that ability.
In truth, even Katakuri himself found it difficult to explain exactly how he had awakened it.
As for awakening it in battle against Katakuri like Luffy had, Sarutobi Hiruzen was far too strong to feel any pressure at all. Naturally, there could be no breakthrough between life and death.
"It'll be difficult to make further progress with Observation Haki