One Piece: Dream of Immortality - Chapter 2: It can’t be true!

A con-man and policewoman that are legends of their respective professions suddenly die, then are reincarnated and return to the Tang Dynasty of ancient China as little kids.

Accepting their second chance and forced restart, they choose to use the modern knowledge and specific talents that they have in their previous lives in order to live comfortably in this new life.

- Description from Novelupdates

I am the sword.

Killing a man amidst a thousand miles, no one dares take ten steps.
Killing a man amidst a thousand miles, no one can take ten steps.
Killing a man amidst a thousand miles, ten steps? Not possible!

I am the sword, the sword is me,
On the path towards heaven, each shall wield their own.

- Description from Novelupdates

Hou Niao, devoted to seeking the Dao, found himself mistakenly sent as an undercover agent to the Demon Sword Sect, eagerly anticipating the day he’d be rewarded for his service and could return to the Daoist Sect… Only when he had become a towering figure in the Sword Dao did he sorrowfully realize that there was no one left with the power to recall him!