Land of Fire border.
Kakuzu did not return to Konoha with Might Guy.
He brought the boy he had rescued from the ruins to the outskirts of an even more remote village, one that had long since been abandoned. The campfire crackled, casting their silent figures against the broken walls, where they swayed unsteadily.
The boy woke amid the jolting journey. Looking at the masked man before him, whose green eyes were the only part of his face visible, fragments of memory began to come together. He remembered the battle that had devastated everything, and he remembered those arms carrying him out of the collapsed rubble.
"Thank you..." The boy's voice was dry and weak, yet filled with sincere gratitude. Struggling to sit up, he said to Kakuzu, "I... I want to follow you."
Kakuzu did not even look up. He continued examining the boy's wounds, and only after confirming there were no signs of infection did he coldly spit out a few words. "I'm not a good person. Saving you was just convenient."
Yet the boy was unusually stubborn. Looking at Kakuzu, he repeated, "I have nowhere else to go. Please take me with you."
Kakuzu's movements paused. He remained silent for so long that the campfire let out a sharp pop. Suddenly, he felt old.
He took several standard kunai and a few shuriken from his pocket and threw them onto the ground before the boy. Metal struck metal with a crisp clang.
"First, learn how to kill."
Kakuzu's teaching methods were simple to the extreme, and brutal to the extreme. There was no theory, no foundation—only the purest, most efficient techniques for killing.
He grabbed the boy's hand and forcibly made him grip a kunai, demonstrating again and again.
"Here is the throat. Stab in, twist, pull