Gu Changtian accidentally travels to the world of One Piece and is bound to the One-Punch Man Summoning System. In the One Piece world, he establishes the First Legion and continuously accumulates shock points.

Such a terrifying demon has crossed over into the world of One Piece. What will become of the One Piece world...?

"The Warring States period was terrifying; the First Legion members were all like monsters..."

Whitebeard: "Giants are the strongest men in the world..."

Redhead: "Oh no, my pride isn't working anymore..."

Garp: "Even my iron fist can't beat the First Legion..."

Kizaru: "No matter how much money you offer me, I won't fight the First Army..."