One Piece - I Am A Different Luffy! - Chapter 3 - 2 - Where Am I?

Before his death, he was the only sword cultivator in the whole world, who dedicated his entire life to the path of sword immortality.

When he opened his eyes again, the world had completely changed. He began to cultivate the path of sword immortality again, slaying the heavenly way, shattering the universe with his will, and achieving the realm of sword immortality!

- Description from Novelupdates

The protracted ’witch hunting’ had faded into silence with the end of the Seven Years’ War, and the mysteries of the East Coast had begun to conceal themselves, yet gunpowder was on a rapid rise. Mo Qishang, who should have been utterly confounded, stood at the crossroads of destiny in the name of Arthur. He stared in astonishment at the charging knights, the wizards atop the high towers, and the bizarre wilderness. He felt the sharpness of the longsword and the recoil of the firearm, both clear and unfamiliar. At last, he excitedly shook his robe and, with a smile on his face, said— “Do not believe what I say, for to believe is to exist!”

Read at least six chapters, then prepare to crave the rest.The main character will show up in Chapter Five, though I don't recommend skipping the first four chapters.-----The world was celebrating. The Demon King was dead, along with his Darkness Generals.Humans led the other races to war for subjugation. They killed all, and none were spared. However, thousands of years before this happened, a piece of history was altered by time itself. In fact, the Demon King didn't have four generals but only one, which he sealed and sent into eternal slumber. Just as he started to close his eyes, the chains locked away for eternity shattered into pieces.

Born into a unique world where villages fight to gain power and control, the main character, Shi Hao, is a genius blessed by the heavens born under the poorest of conditions. His clan, however, has a mysterious past. To rise up and become the genius he is meant to be, the clan goes through every effort to aid his cultivation as they battle through fanatical monsters and engage in power struggles with other clans. His journey will bring him through unknown lands until he is able to become a person that can truly shake the world.