Naruto: After a Thousand Years of Immortality, I Outlived the Third Hokage

[Hokage + Playing It Safe + Immortality + Behind the Scenes + Invincible + Investment]

He transmigrates to the Warring States period, becomes an ordinary member of the Senju clan, and awakens an Immortality System. Fighting is dangerous, so he'd rather make a cup of tea and watch the show.

He witnessed Hashirama and Madara end the era of chaos, and even advised the Second Hokage, Tobirama, on developing forbidden techniques.

He once invested in a young Jiraiya, and got Perfect Sage Mode in return.

He once saved Tsunade's dying younger brother, and got top-tier Medical Ninjutsu in return.

As everyone else grows old and dies, he remains young.

When Pain descends on Konoha, he finds that a janitor, an old man, flicks Shinra Tensei away with a single finger.

"Young man, stop thinking about causing destruction all the time. I know the history of the ninja world better than you do."