Straight to the point, who might know that the red-hair Shanks has a daughter? One of the four emperors of the sea, one of the most fan-favourite characters who sacrifices his hand for the rubber boy, has a daughter. And the daughter is an idol superstar.
Straw Hat Luffy and his infamous nakamas continue their journey while they make short visit outside of the main storyline, and that’s what an anime movie usually does. During their journey, they stop at an island famous for its music and coincidentally there is a concert there with a lot of people attend the concert.