After suffering great personal loss during the battle of Marineford, Monkey D. Luffy finds himself stranded on Rusukaina, a treacherous island crawling with huge and dangerous creatures. There, he has committed himself to a two-year stretch of training to learn "Haki," the energy that combatants can use to grant themselves a variety of abilities in battle. Luffy is jerked away from his otherwise peaceful training by the abduction of Sandersonia and Marigold, sisters of his friend and ally Boa Hancock. With Boa's aid, Luffy seeks to track down the infamous pirate responsible for the kidnapping, a man whose recent prison break is the result of Luffy's own reckless actions. Luffy must use his developing grasp of Haki to defeat this new foe while coming to terms with his overbearing grief in the process. The special takes place during the two year before the Straw Hats reunite on Sabaody. Luffy is currently in Rusukaina training to get stronger to take on the New World. However the training is interrupted when Hancock's sisters, Marigold and Sandersonia, are kidnapped by the Byrnndi World, a pirate who was locked away on Level 6 of Impel Down but escaped during Luffy's invasion to save Ace, in order to lure Hancock to him and use her as a hostage against the World Government due to her Shichibukai status. Thus Luffy and Hancock head off to confront him and save Hancock's sisters.