One Piece: King of the World - Chapter 451: The Undercurrent Surges from All Directions

It begins on the mountain.

With the glint of a knife, a flash of steel in the hands of a sworn brother. A betrayal.

Stabbed and pushed down the mountain, Zi Chen lied within the red-stained snow, left to die.

This is where it begins; he is given life by lightning,
baptized by thunder.

Those who had once betrayed him should all suffer in his cruel revenge.

- Description from Novelupdates

A man with a lifelong martial arts background, raised in Asia due to his family's profession, moves to the US for education and work. He discovers Historical Medieval Battles through a colleague and becomes deeply passionate about it. He trains hard and becomes skilled enough to represent his country.During a competition, his armor fails, and he's struck in the head with a two-handed axe, seemingly dying. But is this truly the end?