The Impel Down Arc is the twenty-first story arc in the series, and the third in the Summit War Saga of the One Piece series, continuing from the Amazon Lily Arc. Luffy puts off finding his crew in favor of rescuing his brother Ace from the underwater prison Impel Down. With some assistance from Boa Hancock, he manages to infiltrate the facility. However, fulfilling his objective and escaping the hellish prison might be easier said than done. Following Luffy's and Hancock's entrance on the ship, Hancock demands for more food. They bring it to her, and she uses her Mero Mero no Mi to freeze the Marines that peek into her room, so they would not see Luffy as a stowaway. Luffy eats all the food, and remarks how delicious it is. The Marines outside heard it, and think someone else is in there and betting that if Hancock had said that, they would shave their hair into mohawks, but Hancock emerges with a few huge plates on a cart, remarking that she was stuffed as the Marines stare in awe (and they all get mohawks).

Meanwhile, many powerful Marines, (including Smoker, Tashigi, Hina, Jango, Fullbody, Comil, T-Bone, John Giant, Kizaru, and Aokiji) are gathering at Marineford to prepare to combat Whitebeard following the destruction of their observation ships. At Mariejois, five of seven Shichibukai are gathered, Donquixote Doflamingo, Blackbeard, Gekko Moriah, Bartholomew Kuma, and Dracule Mihawk, who are eating with a few Marines. Off to the side, Garp is talking to Ace, saying that even if Ace was killed right there, it would not do any good because they would not be able to stop Whitebeard, saying that they have already angered the "Ruler of the Seas". Garp continues on, expressing his disappointment that both Luffy and Ace turned to piracy when he wished for them to be Marines. Ace counters it would not have mattered anyway since they have the blood of a world class criminal in them. He goes on further explaining that he took his mother's name "Portgas" out of love for her and does not care in the slightest of his father, claiming Whitebeard to be his only true father.