NARUTO: Woke Up in the Warring States Era with a Simulation System

DISCLAIMER & STORY TAG
Acronym: N.W.W.S.S. (Naruto: Woke Up in the Warring States Era with a Simulation System)

Rights Notice:
"Naruto" and all canon characters, jutsu, settings, and lore are the exclusive property of Masashi Kishimoto, Shueisha, Shōnen Jump, TV-Tokyo, and VIZ Media.
We claim zero ownership of the Naruto franchise; this is a non-commercial fan-fiction written purely for fun under fair-use/fan-work guidelines.
The only character we legally own is UZUMAKI KŌSEN (original protagonist) and any original supporting characters, plot deviations, or system mechanics created for this story.

What the story is about:
A college drop-out from our world wakes up in the body of Uzumaki Kōsen, a red-headed teen conscript fighting for the Senju clan during the blood-soaked Warring States Era.
Every time he dies on the battlefield-usually at the hands of Uchiha Izuna-time rewinds (or shifts to an identical timeline). Only Kōsen keeps his memories, muscle memory, and the skills he trained.
Armed with a mysterious "simulation system" that logs stats, doles out pain at 97 % fidelity, and offers cryptic hints, he grinds through loop after loop to master kenjutsu, chakra chains, water-style, and battlefield tactics-while trying to keep the world spinning long enough to see an actual tomorrow.
It's equal parts ground-level war story, overpowered training montage, and dark comedy about a guy who can't stay dead and refuses to stop experimenting on destiny-until the day the reset fails and history has to live with what he's become.