One Piece: Human God - Chapter 31: Sky Island Fight II

Choi Hyun-seok, a heavyweight champion of the biggest mixed martial arts league on Earth and the one who was called the strongest had died.Afterwards, he was granted new life as a hero in another world.‘Wealth! Honor! Endless beauties at your fingertips!’With thoughts of such a dazzling future, the first thing that he saw when he came to this new world was a towering ox monster.The monster, who was the commander of the demon army, asked.“Hero? You’re saying you’re the hero?”“Uh…I think…?”And so, that was the start of hell.

One day, I was given the mysterious power of Hwanmong.

There was once an immortal cultivator fighting for the fate of human beings. Unfortunately, he failed that time; but fortunately got another chance as he was reborn once more as a human, on the earth of 5,000 years ago. With a second chance, he not only would embark on the road of saving all mankind, but also would retrieve his human nature on the new journey that would last for 5,000 years.

- Description from Novelupdates

A mental patient, or a born policeman?

A peerless genius, or a master of crime?

There are cops who are least like cops, and there are criminals who are least like criminals.

Neither good nor evil is absolute.

It is a grey world we live in.

- Description from Novelupdates