One Piece: I Have the Swim-Swim Fruit

The protagonist is a young man from a modern city who transmigrates to the world of Pirate King after an accident, only to discover that he has become a Logia-type Water-Water Fruit Devil Fruit User. His abilities let him liquefy his body, control currents, and trigger all kinds of water-based phenomena. In the early days of the world of Pirate King, he is no powerhouse, but starts from scratch. By developing his abilities over water, he gradually recruits a crew, clashes with the Straw Hat Pirates, contends with the World Government, and may even overturn the balance of power across the entire world.