A Life-threatening Break-in! The Underwater Prison Impel Down!

Deep inside Impel Down, Garp boasts to Ace about some of Luffy's recent doings and remarks that, as a world-class criminal's offspring, the two brothers carry that same blood. Ace counters that Whitebeard alone counts as his father, the one who looked after him once he had gone wild. Far off at sea aboard Momonga's ship, Luffy worries over Ace while hidden beneath Hancock's disguise. Up on deck, Momonga spots a vessel that strikes him as familiar and recognizes it as Buggy's; that crew, shaken by a Sea King rising beside them, weighs storming the prison to liberate their captain before Alvida's suggestion of a small boat convinces them the venture is far too dangerous and they abandon it.

Among the tortured inmates a fresh arrival refuses another prisoner's command, igniting a fight, and the creature Minotaurus hauls the pair off to a separate cell to be eaten alive. Passing through the Gate of Justice, Momonga's ship anchors amid a host of other Marine vessels, and the sheer crowd of them leads Luffy to wonder whether a Buster Call might have been ordered. Stepping off the ship, Momonga and Hancock head inside with the hidden Luffy in tow, the empress straining to tolerate the guards' adoration as Momonga gently asks her not to petrify them. Right around then, Buggy the Clown slips out of his cell on Level 1.

At the prison gate, the deputy warden Hannyabal welcomes Momonga and Hancock and tells him he wishes to see Warden Magellan, while Vice Jail Manager Domino escorts the empress to a room for the private search applied to every visitor. Treating the task seriously, Domino locks Seastone handcuffs onto Hancock to shut off her Devil Fruit ability, and the empress complies despite her heart pounding with tension. This entry opens the Impel Down Arc and introduces the prison itself along with Pankuta Dakeyan, Minotaurus, Hannyabal, and Domino; the source material spans chapters 525 and 526. When it first aired, the broadcast ended by teasing the feature titled Strong World, part of the One Piece film line, which is also why the usual next-episode trailer ran shorter than normal.