As a child, Monkey D. Luffy dreamed of becoming King of the Pirates. But his life changed when he accidentally gained the power to stretch like rubber...at the cost of never being able to swim again! Years, later, Luffy sets off in search of the "One Piece," said to be the greatest treasure in the world...

Luffy and the princess of Fish-Man Island escape the castle and head to the mysterious Forest of the Sea. Meanwhile, the kingdom is under attack by dark forces. What is the source of the hatred between humans and the merfolk?!