One Piece: Gyojin Tou-hen

Two years after being scattered across the Sabaody Archipelago, Luffy and the Straw Hat crew return to the place where they parted, each transformed by intense training. Before they can sail, they must get past the Marines and expose a band of impostors using their names to recruit followers for a fake Straw Hat crew.

Once reunited aboard the Thousand Sunny, their journey toward the New World takes them beneath the sea to Fish-Man Island. There they enter a society burdened by old wounds between humans and fish-men, while Hody Jones and the New Fish-Man Pirates seek to turn that resentment into a violent uprising. For Luffy and his friends, the island becomes more than another stop on their voyage; it is a place where they must confront a power fed by generations of hatred.