I am, Flame-Chaser of Previous Era - Chapter 58: Extraterrestrial

Crossing to One Piece world, he became Roger’s younger brother.

A former sporting rifle shooter genius transforms into the ‘Juvenile Butcher’. While originally supposed to have received the death penalty, he was instead fortunate enough to have entered a secret and highly regarded armed force, throwing himself into the ‘Nirvana Project’.

After a period of 10 years, he now has time to freely recover. Having trained until he had excellent military and martial skill, he sweeps through various military districts and returns back to his hometown. Under the monitoring of a beautiful female cop, he re-establishes his family’s bodyguard service, protecting beauties and moving unhindered, his achievements causing the fame of his outstanding, god-level bodyguard service to resound across the world!

- Description from Novelupdates

After an unexpected accident, An Luo was reborn as the young master of a business family. Even as his grandfather’s favored grandson, he seems to only be a cannon fodder in the brothers’ struggle to seize power. However, the most frightening thing is… the strange emotions that flicker in his little brother’s eyes as he looks at him. At that moment, overwhelmed by his brother, An Luo angrily thought: Could it be that he is doomed to never escape this vicious cycle of “brotherly love”?

An Luo(frowning): After rebirth, I don’t want to be together with some strange person.

Someone(suddenly appearing in the back, smiling): What did older brother just say?

An Luo: …Nothing.

- Description from Novelupdates

Emperor Zi Yu used 5 strikes of his axe to split mountains and unify everyone underneath the heavens. He partitioned the land into 9 areas, thus establishing the Nine Cauldrons which eventually became known as the 9 prefectures.