Uzumaki Immortal Grand-Uncle

I was reborn as Uzumaki Masahiko, a 48-year-old joke in the Warring States Era. After one embarrassing battlefield debut, I was destined to die of old age before Konoha was even founded. Then, on the eve of my 49th birthday, I discovered the truth of my "useless" System: I don't get older. I get younger. While future legends like Hashirama and Madara are busy fighting, I'm busy reversing my age and collecting "Witness Points" for every major event I see. Witnessed Hashirama & Mito's Wedding? +20 Points! Helped Tobirama name the Hiraishin? +5 Points! Tricked Uchiha Madara with a Level 10 Henge? Priceless! They all think I'm just a goofy old grand-uncle. They have no idea I'm leveling up in secret, waiting to be in my prime when the Fourth Great Ninja War finally rolls around. I'm the man who will live to see the entire show, and this time, I'm not just a witness—I'm a player. — Description from novelcodex.org