Naruto: Starting as Orochimaru's Test Subject!

[Power Fantasy] [Hokage Fanfiction] [Leveling Up by Spending Lifespan] [Fighting Above His Rank] [A Well-Rounded Protagonist] [Reasonable Ability Acquisition]

Lin Feng transmigrates to the Hokage world. When he opens his eyes, he finds himself on an operating table, hovering between life and death, about to face Orochimaru's deadly survival-of-the-fittest battle in Otogakure.

Fortunately, he activates the Lifespan-Spending System at the last minute. All he has to do is expend years of his life to pour knowledge into ninjutsu and science, allowing him to make unlimited deductions and obtain the results for the equivalent amount of time.

"You spend fifty years of your life and improve the Aburame Clan's Kikaichū. From now on, the Kikaichū can absorb Tailed Beast Chakra for you, making you a pseudo-Ten-Tails Jinchuriki."

"You spend three hundred years of your life studying Orochimaru's notes, perfectly cultivating the Mangekyō Sharingan and awakening both Kamui eyes."

"You spend five hundred years of your life awakening the Eight Gates: Gate of Death, and overcome all of its drawbacks."

"You spend two thousand years of your life mastering the Sage Mode of the three great sacred lands, then successfully fuse them together.