Naruto: The Undying Old Man

He transmigrated to the Warring States era of Hokage. Though he had a System, he spent decades achieving nothing, only realizing its true purpose when he was old and frail. When you have an infinite lifespan and watch familiar faces grow from children into the elderly, all you can do is sigh: "How lonely it is to be invincible..."

This novel and its characters are entirely fictional. Any resemblance to real people or events is purely coincidental. Do not imitate.