Naruto System in One Piece - Chapter 8

A seemingly ordinary training exercise led Chen Jian and his squad into a completely different time and space.In the post-apocalyptic world, monsters run rampant, and the surviving humans struggle to live under their terrifying claws.To fight the monsters, the living have abandoned everything.Human nature no longer exists; beastliness is the mainstream.To defeat them, one must first become them.-----------------Chen Jian was supposed to be like the others here, pursuing the maddening evolution.But, when the tungsten-core armor-piercing round first penetrated the Kui Niu's keratin armor, he suddenly discovered...Perhaps there is another way to stay alive?

Kai of the Sorcerer’s Tower is one of the last mages left, barely surviving in a world ruled by creatures of the dark — where the era of mages ended, and most of the lands got contaminated with dead mana. To save his world and fulfil his master’s last wish, he put himself through a forbidden ritual, risking his soul being ripped into pieces to make his way into the past. In an era with abundant mana — an era yet to enter the Golden Era of Magic. Things go wrong, of course, as they always do, and he finds himself thousands of years before the world fell to mana contamination — in the body of a young lord, Arzan. All is not well, though, as the young lord was murdered by someone right at the cusp of a beast wave threatening the territory, while larger threats loom on the horizon. There was a lot to do for Kai to regain his former strength in this time of primitive technology, but then again, he might just be able to change that.

Traveling through the big world that covers the sky, awakening the sign-in system, and rejecting the rich woman’s pursuit at the beginning! Sign in to get a pair of pupils!

Sign in at Daleiyin Temple and get a five-star reward Emperor Seal!

Sign in in the Bronze Immortal Hall and get a seven-star reward for inextinguishable profound art!

Sign in on God and get a ten-star reward Fortune Jade Plate!

The ancient warriors, step on the restricted area, control life and death, and control reincarnation!

The heavens and the world, the rolling red dust, have left his footprints!

The legend of Emperor Xuantian began when the Nine Dragons pulled a coffin on Mount Tai!

- Description from novelbuddy

This is the era where people prioritize science and Martial Dao. After the great disaster, the human race discovered the Ancient Zenith civilization. They entered the Age of Great Cultivation and began their journey to colonize the Kunlun Realm!