After finishing his battle with Obito, Naruto returned to Amegakure.
Konan had witnessed the entire battle through the Telescope Technique.
Captain Yamato had watched it with her.
Yamato had come to Amegakure on a "long-term mission" from Tsunade.
[After careful consideration, the author has decided to discard the premise that Wood Release consumes life force. Tsunade's instructions to Yamato and the circumstances of the First Hokage's death have been revised as follows.]
"Tenzo, Naruto has now mastered my grandfather Hashirama's Wood Release. Wood Release consumes enormous amounts of chakra, but that isn't the real concern. What truly deserves our attention is the healing ability of Grandfather's Cells."
"Hand-Seal-Less Healing is convenient, but that convenience also makes its dangers easy to overlook. There is a limit to how many times cells can divide over a person's lifetime. Once that reaches a certain point, it shortens their lifespan. Even someone as powerful as my grandfather, Hashirama Senju, was helpless against those accumulated side effects, and ultimately died before his time..."
"So, Tenzo, I want you to stay by Naruto's side, keep an eye on him, and remind him often, so he doesn't repeat my grandfather's mistakes. Naruto has already agreed. This is an immensely honorable and demanding mission. What do you say, Tenzo?"
Inside a tower in Amegakure's Southern District.
Captain Yamato earnestly impressed the point on him. "Naruto, even though you can now recover from injuries easily, you should still avoid getting hurt whenever possible. During the Warring States Era, research into cells was very limited. Even the First Hokage, Lord Hashirama himself, didn't know the drawbacks of Hand-Seal-Less Healing."
"That was why he paid little attention to avoiding attacks in battle. Sometimes, the kindhearted Lord Hashirama would even let himself get hurt to spare his opponents' pride!"
"And whenever