One Piece: I Can Sacrifice Devil Fruits

(New author here. The early chapters went off the rails, so feel free to start with Volume Two-it won't affect your understanding of the overall plot.)

He transmigrates into the world of One Piece and opens his eyes inside an iron cage.

Across from him stands an enslaved gladiator wielding a warhammer. The stands are packed with scum driven wild by gambling. His system activates, offering four choices. With no time to hesitate, he chooses equipment.

Heartsteel merges with his body. His bones crack like thunder, and his muscles tear apart and forge themselves anew. From that iron cage, he fights and kills his way to the ends of the world.

System Notification: Slain Devil Fruit users can be sacrificed for random rewards. Not a Devil Fruit user? Killing them yields nothing.

From then on, his rule is simple: anyone who deserves to die goes down with a single punch.

A Marine uniform is nothing more than a legal license to kill.

When his iron fist punches through an Emperor's chest, when his Conqueror's Haki clashes with Red-Haired Shanks's, when a Celestial Dragon kneels amid the ruins and asks, "Who the hell are you?"

He replies, "I'm just a Marine. The kind who only kills scum."